THE UNIVERSITY OF THE SOUTH PACIFIC

Transcription

1 THE UNIVERSITY OF THE SOUTH PACIFIC Evaluation Of Some Management Strategies Against Lepidopterous Pests Of Head Cabbage In Samoa John Bosco Sulifoa November 2007

2 Evaluation Of Some Management Strategies Against Lepidopterous Pests Of Head Cabbage In Samoa by JOHN BOSCO SULIFOA B. Agr (S.Pac.) (2001), PGDAgr (S.Pac.) (2003) A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Crop Science (MSc. Crop Science) at The University of the South Pacific Faculty of Islands and Oceans School of Agriculture and Food Technology Alafua campus Samoa November 2007 i

3 TABLES OF CONTENTS Title page Author statetment of accessibility Author statement of accessibility Part 2 Dedication Declaration List of figures List of tables List of appendices Acknowledgements Abstract i vi vii viii ix x xiii xiv xv xvii Chapter 1: General introduction 1 Chapter 2: Effect of intercropping on damage by leaf-eating caterpillars and yield of head cabbage 5 Abstract 5 2.1: Introduction 7 2.2: Materials and methods : Experimental set up and treatment application : Agronomic practices (Trials 1 and 2) : Data collection : Statistical methods : Results : Incidence of damage by leaf-eating caterpillars 15 ii

4 2.3.2: Incidence of infestation by each species of caterpillar : Incidence of infestation by Crocidolomia pavonana : Incidence of infestation by Hellula undalis : Incidence of infestation by Spodoptera litura : Severity of damage to cabbage heads by leaf-eating caterpillars (at harvest) : Number of cabbage heads harvested per plot : Total weight of cabbage heads harvested per plot : Number of marketable cabbage heads : Discussion 38 Chapter 3: Relative susceptibility of four head cabbage varieties to infestation by leaf-eating lepidopterans 43 Abstract : Introduction : Materials and methods : Experimental set up : Agronomic practices : Data collection : Statistical methods : Results : Incidence of damage by leaf-eating caterpillars : Incidence of infestation by each species of caterpillar on four cabbage varieties 51 iii

5 : Incidence of infestation by Crocidolomia pavonana Seasons 1 and : Incidence of infestation by Hellula undalis Seasons 1 and : Incidence of infestation by Plutella xylostella Season : Incidence of infestation by Spodoptera litura Season : Severity of damage to cabbage heads by leaf-eating caterpillars (at harvest) : Number of cabbage heads harvested per plot : Total weight of cabbage harvested per plot : Number of marketable cabbage heads : Discussion 61 Chapter 4: Effects of some crude aqueous plant extracts on the survival of Crocidolomia pavonana (Fabricius) 65 Abstract : Introduction : Materials and methods : Rearing of C. pavonana larvae for testing plant extracts : Treatments : Testing of plant extracts on C. pavonana : Collection of data : Statistical methods : Results : Survival of cabbage C. pavonana : Level of damage to cabbage leaves 80 iv

6 4.4: Discussion 84 Chapter 5: Predication of diamondback moth larval infestations of cabbage by means of pheromone trapping 87 Abstract : Introduction : Materials and methods : Pheromone trapping : DBM larval infestations : Statistical methods : Results : Discussion 94 Chapter 6: Summary and conclusion 97 References 103 Appendices 113 v

7 Author Statement of Accessibility The University of the South Pacific Library Name of candidate : Degree : Master of Science in Crop Science Department/School : School of Agriculture & Food Technology Thesis Title : Evaluation of some management strategies against lepidopterous pests of head cabbage in Samoa Date of completion of requirements for award : This thesis may be consulted in the library without the author s permission. 2. This thesis may be cited without the author s permission provided it is suitably acknowledged. 3. This thesis may be photocopied in whole without the author s written permission. 4. This thesis may be photocopied in proportion without the author s written permission. Under 10% 40 60% % 60 80% % Over 80%.. Yes/No Yes/No Yes/No Yes/No 5. I authorize the University of the South Pacific (USP) to produce a microfiche copy for retention and use in the library according to rules 1 4 above (for security and preservation purposes mainly). 6. After a period of 5 years from the date of publication, the USP library may issue the thesis in whole or in part, in photostat or microfilm or other copying medium, without first seeking the author s permission. 7. I authorize the University to make this thesis available on the internet for access by USP authorized users. Yes/No Yes/No Yes/No Signed: Contact Address: Ministry of Agriculture, Samoa Date:. Permanent Address: vi

8 u The University of the South Pacific Library Author Statement of Accessibility - Part 2 - Permission for Internet Access Name of Candidate Degree DepartmentISchool Institution/University Thesis Title Date of completion of requirements for award Master of Science in Crop Science School of Agricultzrre & Food Technology fie University of the South Pacflc Evaluation of some management strategies against lepidopterous pests of head cabbage in Samoa 2 11 /flmfl4 62-e 2 l; L) I authorize the University to make this thesis available on the Internet for acess by USP authorized users. 2. I authorize the University to make this thesis available on the Internet under the International Digital Theses Project. Signed:.. Date: ;7(... /vl~c~c~&~--a -?'L'L)& Contact Address: Ministry Of Agriculture, Samoa Permanent Address:... vii

9 DEDICATION To my dearest wife Ramona Sulifoa and loving children Rosemary Sulifoa & Richard Andrew Sulifoa viii

10 DECLARATION I, John Bosco Sulifoa (S ), hereby declare that this thesis represents my original research. The entire work described herein, except as otherwise acknowledged in the text, has not been submitted, whether in part or fully, for higher degree at this or any other University. Date: John Bosco Sulifoa Confirmation of Declaration I hereby confirm the declaration of originality of this work by the author, Mr. John Bosco Sulifoa (S ), who worked under my direct supervision. Date: Dr. Adama A. Ebenebe (Ph.D.) (Principal Supervisor) ix

11 LIST OF FIGURES Page Figure 2.1a: Incidence of damage by leaf-eating caterpillars in different cropping patterns- Trial 1 16 Figure 2.1b: Incidence of damage by leaf-eating caterpillars in different cropping systems- Trial 2 18 Figure 2.2a: Incidence of infestation by Crocidolomia pavonana - Trial 1 20 Figure 2.2b: Incidence of infestation by Crocidolomia pavonana - Trial 2 21 Figure 2.3a: Incidence of infestation by Hellula undalis - Trial 1 23 Figure 2.3b: Incidence of infestation by Hellula undalis - Trial 2 25 Figure 2.4: Incidence of infestation by Spodoptera litura - Trial 1 26 Figure 2.5a: Severity of damage to cabbage heads by leaf-eating caterpillars at harvest - Trial 1 28 Figure 2.5b: Severity of damage to cabbage heads by leaf-eating caterpillars at harvest - Trial 2 29 Figure 2.6a: Number of cabbage heads harvested from 12 data plants/plot - Trial 1 30 Figure 2.6b: Number of cabbage heads harvested from 12 data plants/plot - Trial 2 31 Figure 2.7a: Total weight (g) of cabbage heads/plot - Trial 1 33 Figure 2.7b: Total weight (g) of cabbage heads/plot in Trial 2 34 Figure 2.8a: Mean number of marketable heads of cabbage harvested per plot - Trial 1 36 Figure 2.8b: Mean number of marketable heads of cabbage harvested per plot - Trial 2 37 Figure 3.1a: Incidence of damage by leaf-eating caterpillars on four cabbage varieties - Season 1 49 Figure 3.1b: Incidence of damage by leaf-eating caterpillars on four cabbage varieties - Season 2 50 x

12 Figure 3.2a: Incidence of infestation by Crocidolomia pavonana on four head cabbage varieties - Season 1 52 Figure 3.2b: Incidence of infestation by Crocidolomia pavonana on four head cabbage varieties - Season 2 52 Figure 3.3a: Incidence of infestation by Hellula undalis on four head cabbage varieties - Season 1 54 Figure 3.3b: Incidence of infestation by Hellula undalis on four head cabbage varieties - Season 1 55 Figure 3.4: Incidence of infestation by Plutella xylostella on four head cabbage varieties - Season 2 56 Figure 3.5: Incidence of infestation by Spodoptera litura on four head cabbage varieties - Season 1 57 Figure 3.6: Severity of damage to cabbage heads by leaf-eating caterpillars (at harvest) - Seasons 1 and 2 58 Figure 3.7: Mean number of cabbage heads harvested/ plot - Seasons 1 and 2 59 Figure 3.8: Total weight (g) of cabbage heads/plot - Seasons 1 and 2 60 Figure 3.9: Mean number of marketable heads harvested from each plots - Seasons 1 and 2 61 Figure 4.1: Mortality of Crocidolomia pavonana larvae exposed to cabbage leaf pieces treated with different crude aqueous extracts of plants - Experiment 1 79 Figure 4.2: Mortality of Crocidolomia pavonana larvae exposed to cabbage leaves treated with different concentrations of crude aqueous extracts of kava root powder and basil leaves - Experiment 2 79 Figure 4.3: Effects of different crude aqueous extracts of plants on level of damage to cabbage leaves by Crocidolomia pavonana at 72 hours after introduction of larvae Experiment 1 82 Figure 4.4: Effects of different concentrations of kava powder and basil leaf extracts on damage caused to cabbage leaves by Crocidolomia pavonana at 72 hours after introduction of larvae Experiment 2 82 Figure 5.1: Mean weekly catches of Plutella xylostella adults per pheromone xi

13 trap and mean weekly counts of larvae per plant at Aleisa 92 Figure 5.2: Mean weekly catches of Plutella xylostella adults per pheromone trap and mean weekly counts of larvae per plant at Alafua 93 xii

14 LIST OF TABLES Table 4.1: Pesticidal properties of some commonly occurring plants in Samoa 70 Page xiii

15 LIST OF APPENDICES Page Appendix 1: Statistical anaylsis of transformed data for chapter 2 (intercropping trial) 113 Appendix 2: Field plots showing damage to the four head cabbage varieties tested in the relative susceptibility experiment 122 Appendix 3: Characteristics of the four cabbage varieties used in chapter 3 (varietal trial) 123 Appendix 4: Statistical analysis on transformed data for chapter 3 (varietal trial) 124 Appendix 5: Toxicity data for some chemical components found in plant genera used in the plant extract experiment 129 Appendix 6: Statistical analysis on data for chapter 4 (plant extract experiment) 130 Appendix 7: Pictures showing the effect of different treatments on C.pavonana larval feeding activities at 6 hours (plant extract experiment) 137 Appendix 8: Pheromone traps near cabbage fields 139 Appendix 9: Statistical analysis on data for chapter 5 (pheromone trapping) 140 xiv

16 ACKNOWLEDGEMENTS First of all, I would like to thank the Almighty God for his protection upon me, which has brought me to this stage. I would like to express my sincere gratitude and appreciation to the following people for their support and encouragement throughout this research: I would like to acknowledge and thank my project supervisor, Dr. Adama A. Ebenebe, for all the assistance, supervision and constructive comments during this research study, which enabled me to complete this thesis. The University of the South Pacific for providing funds for the research. Mr. Ian Faleono and Mr. Peni Misipati (USP technicians - Crop Science section) for assisting me during my field work. Mr. David Hunter, for helping me with my data analysis. My Solomon Islands colleagues: Mr. Francis Waelesi, Mr. Gilbert Forres, Mr. Simon Iro Sefa, Mr. Simon Baete, Mr. George Boe, and Mr. Crispus Ramofaga, for helping me with my field work. My father and mother, for encouragement and understanding, which have helped me to carry on even though this world presents many challenges. My father-in-law, for all the help that he gave me, particularly in providing some of the materials that I used for my experiments. My dearest wife, Ramona Sulifoa; you are my back bone, always standing beside me through the tough times that we have been through. Your support in terms of word and field work helped me to complete this thesis. xv

17 Finally, I would like to thank those who are not mentioned here, but who contributed to this research project. xvi

18 ABSTRACT Four main areas of investigations were conducted at the University of South Pacific, School of Agriculture and Food Technology, Samoa, towards this research project. These were (1) effect of intercropping cabbage with tomato and cabbage with yardlong bean on damage and infestations by leaf-eating caterpillars on head cabbage, (2) susceptibility of four cabbage varieties ( KK cross, Eureka, Racer drumhead, Copenhagen market ) to leaf-eating caterpillars of head cabbage, (3) effects of some crude plant extracts on damage to cabbage and survival of Crocidolomia pavonana larvae, and (4) pheromone trapping for monitoring Plutella xylostella infestations in a cabbage crop. Results from the intercropping study indicated that cabbage/tomato intercrop reduced incidence of damage and infestation by the caterpillars compared to unsprayed monocrop cabbage, but yield from the intercrop was much lower than that of monocrop cabbage sprayed with a commercial insecticide (indoxacarb). Combining cabbage/tomato intercropping with insecticide application resulted in more effective control of the caterpillars than insecticide application to monocrop cabbage alone. In the varietal trial, KK cross showed more resistance to the caterpillars than the other varieties tested, but the final yield in this variety was still very low due to caterpillar damage. In the plant extract experiments, larval mortality in each plant extract treatment was higher than in the untreated control, and kava extract was more effective than the other extracts. Also, damage to cabbage leaves was less in the plant extract treatments than the untreated control, and lower in the kava treatments than the other extracts. For the pheromone trapping study, there was a positive correlation between moth catches in traps and larval infestations in a cabbage crop. The implications of the above findings are discussed. xvii

19 CHAPTER 1 GENERAL INTRODUCTION Head cabbage, Brassica oleracea L., is one of the most important vegetables grown in Samoa, and demand for it is high in the market. Many farmers grow it for sale and for domestic consumption. It is mainly cooked and consumed in soups, or eaten raw in vegetable salads. Several types of pests affect head cabbage production in Samoa; among them are the leafeating caterpillars Spodoptera litura F. (Lepidoptera: Noctuidae) (taro armyworm), Hellula undalis F. (Lepidoptera: Pyralidae) (cabbage webworm), and Plutella xylostella L. (Lepidoptera: Plutellidae) (diamondback moth) (Hollingsworth et al., 1984; Anonymous, 1996), as well as Crocidolomia pavonana F. (Lepidoptera: Pyralidae) (cabbage cluster caterpillar) (Waterhouse and Norris, 1987; Panapa, 2003). According to Hollingsworth et al. (1984) and Anonymous (1996), diamondback moth has become the most destructive insect of head cabbage and other cruciferous plants in Samoa. The same is true of the rest of the South Pacific (Maddison, 1982; Waterhouse and Norris, 1987; Waterhouse, 1992) and the world (Talekar and Shelton, 1993). The annual cost for managing it throughout the world was estimated to be US $1 billion (Talekar and Shelton, 1993). The difficulty of managing diamondback moth is largely because of its ability to develop resistance to synthetic insecticides used against it (Talekar et al., 1985, 1990; Raju, 2005; Zhao et al., 2006). Insecticide resistance in this pest, and control failures against it, are now common in tropical climates such as parts of 1

20 Southeast Asia, Central America, the Caribbean and Southern United States (Talekar and Shelton, 1993). According to Talekar and Shelton (1993), economic production of crucifers has become impossible in some of these areas. Another factor is the destruction of natural enemies due to insecticide application. It is obvious that synthetic insecticides do not provide a sustainable way of managing this pest. Spodoptera litura is an important pest of cabbage in Samoa (Taefu, 1977; Hollingsworth and Aloalii, 1985; Kuma, 2007) and most of the South Pacific (Waterhouse and Norris, 1987, Kuma 2007). It is also an economically important pest of other important crops (Hill, 1983) including taro, tomato, eggplant and banana, which are grown in Samoa (Aukuso et al., 1986). Hellula undalis is also an important pest of cabbage in Samoa (Hollingsworth et al., 1984; Anonymous, 1996) and other countries of the South Pacific (Waterhouse and Norris, 1989; Kessing and Mau, 2007). It is economically important because it causes serious damage to the seedlings (Hollingsworth et al., 1984), and entire seedlings can be destroyed (Anonymous, 1930; Kessing and Mau, 2007). Crocidolomia pavonana is another important cabbage pest in Samoa (Waterhouse and Norris, 1987; Panapa, 2003). It is also a serious pest in the rest of the Pacific region (Fullerton, 1979; Freres and Atalifo, 2000) and in other tropical and subtropical regions of the world (Rueda and Shelton, 1995). C. pavonana is important because even a single 2

21 larva can destroy an entire plant by feeding on its growing points (Rueda and Shelton, 1995; Freres and Atalifo, 2000). The most commonly used approach by farmers to control these insects, worldwide and even in Samoa, is synthetic insecticides. However, the overwhelming consensus around the world is that these chemicals alone do not achieve sustainable management of the pests. Moreover, pesticides have a negative impact on income, health and the environment. Therefore, an integrated management approach, based on careful evaluation and selection of location-appropriate management tools, is increasingly being advocated as the best way for achieving sustainable management of these pests. In view of problems associated with pesticide use, especially the development of insecticide resistance as observed in diamondback moth (DBM) (Plutella xylostella), alternative methods of control (intercropping, host resistance, botanical pesticides, biological control, etc.) have been, and are still being, explored against cabbage pests. For instance, intercropping cabbage with tomatoes was reported to reduce damage to cabbage by diamondback moth (Sivapragasam et al., 1982). Gunawan (1975) tested six head cabbage cultivars (RvE 37, Osena, Yoshine 1, Yoshine 2, Ky cross, and KK cross) against diamondback moth and reported that KK cross was the least infested of the varieties tested. Extracts from neem seeds/neem seed kernels were reported to give good control of diamondback moth in cabbage and other crucifers (Moncada and Sanchez, 1990; Facnath, 1999). Similarly, Derris malaccensis root extract was reported to have some effect against P. xylostella, S. litura and C. pavonana (Crooker, 1979). Based on 3

22 studies conducted in New Zealand, Walker et al. (2003) reported that pheromone trapping might be useful for identifying risk periods when DBM larval numbers in cabbage crops are likely to increase to damaging levels. In India, Reddy and Guerero (2000) observed that an IPM program for DBM, based on pheromone trap catch threshold, natural enemies and selective use of insecticides was more effective in reducing damage compared to management programs based solely on synthetic insecticide use. Although several studies have been conducted on the use of alternative, non-synthetic pesticide methods for controlling lepidopteran pests of cabbage (Crooker, 1979; Timbilla and Nyako, 2000; Walker et al., 2003), none has been reported from Samoa. Therefore, the broad aim of this research project was to investigate the effectiveness of some nonsynthetic pesticide methods (i.e. methods other than synthetic pesticides) for the sustainable management of lepidopteran pests of head cabbage in Samoa. The main areas for investigation were intercropping systems, varietal susceptibility, use of plant aqueous crude extracts as natural pesticides, and pheromone trapping for monitoring pest infestations. 4

23 CHAPTER 2 EFFECT OF INTERCROPPING ON DAMAGE BY LEAF-EATING CATERPILLARS AND YIELD OF HEAD CABBAGE ABSTRACT This experiment was carried out at the University of the South Pacific, School of Agriculture and Food Technology, Samoa, during 2004 and Two trials were conducted to determine the effect of some intercropping systems, and combination of intercropping and insecticide application, on leaf-eating lepidopteran infestation, damage, and yield of head cabbage. In the first trial, tomato and yardlong bean were intercropped, separately, with cabbage (variety Racer drumhead ). In the second trial, only cabbage/tomato intercrop was used, with some modifications in the arrangements of plants within plots. Cabbage/tomato intercrops with insecticide applications were also included in the second trial. Randomised Complete Block Design (RCBD) was used in both trials. Results from both trials showed that intercropping cabbage with either tomato or yardlong bean lowered the incidence of infestation and damage caused by the caterpillars and produced relatively higher yield than unsprayed cabbage monocrop. Cabbage/tomato intercrop performed slightly better than cabbage/yardlong bean intercrop in this regard. However, none of these differences was statistically significant (at P=0.05). In Trial 2, combining intercropping with insecticide application resulted in lower incidence of damage and infestation than in cabbage monocrop treated with insecticide at the same dosage and frequency. These results indicated that intercropping head cabbage with either tomato or yardlong bean could not provide adequate control of the caterpillars in the cabbage crop. However, the intercrops appear to improve the level 5

24 of control achieved with insecticides and can be combined with other control methods in an IPM programme. 6

25 2.1 INTRODUCTION Lepidopterans such as diamondback moth (Plutella xylostella), cabbage cluster caterpillars (Crocidolomia pavonana), cabbage center grub (Hellula undalis) and taro armyworm (Spodoptera litura) are the major pests that affect head cabbage production in Samoa (Hollingsworth et al., 1984; Anonymous, 1996; Panapa, 2003). To control these lepidopterans and produce good quality cabbages, farmers in Samoa use a lot of synthetic pesticides. However, the overwhelming concern around the world is that these chemicals alone do not achieve sustainable management of the pests. In fact, some of these pests have built up resistance to many of the chemicals, which makes it very difficult to control them (Talekar et al., 1985, 1990; Talekar and Shelton, 1993; Raju, 2005). Moreover, synthetic pesticides have a negative impact on income, health and environment. Generally, intercropping is considered a sustainable and environmentally friendly farming system. Intercropping has a multifunctional role and can potentially provide a number of eco-services within the farming systems (Altieri, 1999; Sullivan, 2003). It helps in the recycling of organic materials, water management and protection of soil from soil erosion. There are numerous studies on the effect of intercropping on pest attack. According to Andow (1991), out of 209 studies involving 287 insect pest species, the population of pest insects in intercropping systems was lower in 52% of the studies (149 species) and higher in only 15% (44 species), compared to monoculture. The same author also stated that the population of natural enemies of pests was higher in the intercrop in 53% of the 7

26 studies and lower in only 9%, compared to monoculture. Some of the studies that have reported the beneficial effects of intercropping in reducing insect pest damage include Buranday and Raros (1973), Nickel (1973), IRRI (1974), Karel et al. (1982), Srinivasan and Krishna Moorthy (1992), and Timbilla and Nyako (2001).. There are several reports that refer specifically to the benefits of intercropping for managing cabbage leaf-eating caterpillars. For instance, intercropping cabbage with tomatoes is reported to reduce damage to cabbage by several pests, including diamondback moth (Vostrikov, 1915; Buranday and Raros, 1975; Sivapragasam et al., 1982). Similarly, intercropping cabbage with garlic (Hooks and Johnson, 2002), cabbage with tomatoes, dill, garlic, safflower, and oat, together (Talekar et al., 1985), tansy with broccoli and cabbage (Brewer and Ball, 1979), and cabbage with onion, spearmint (Mentha spicata) and tomato (Timbilla and Nyako, 2001), gave some control of diamondback moth. Varela et al. (2003) stated that intercropping cabbage and tomato reduced diamondback moth and cabbage moth (C. pavonana) attack on cabbage. Srinivasan and Krishna Moorthy (1992) have also found that mustard-cabbage intercrop significantly reduced infestation by diamondback moth, leaf webber (C. pavonana), and H. undalis, in India. Intercropping affects the host-finding behaviour of pests because non-host plants act as physical barriers and produce chemical smells that interfere with the pest s ability to locate its host (CABI, 2000; Stoll and Vellag, 2000). Intercropping also improves the condition for the development and survival of natural enemies, which increases their 8

27 population, which in turn helps to reduce the population of the pest (CABI, 2000; Stoll and Vellag, 2000). There are also reports (Karungi et al., 1999; Nampala et al., 1999; Boucher, 2004) that intercropping, combined with some pesticide use can control pests to below economic levels and help to reduce the application of pesticides. For instance, according to Nampala et al. (1999), intercropping cowpea and sorghum, with minimal insecticide application, increased grain yield in Uganda. The present study was conducted to determine the effects of some intercropping systems on infestation and damage by leaf-eating lepidopteran pests of head cabbage. In addition, the study investigated the effect of combining intercropping and insecticide application on infestation and damage by the lepidopterans. The specific objectives of this study were as follows: To compare the incidence of damage by leaf-eating caterpillars and incidence of each species of caterpillar, and yield of head cabbage, in cabbage intercropped with tomato, cabbage intercropped with yardlong bean, unsprayed and sprayed monocrop cabbage. To assess the effect of plant arrangement in an intercrop on infestation and incidence of damage. 9

28 To evaluate the effects of combining intercropping with insecticide application on infestation and damage by leaf-eating caterpillars. The choice of crop combination in the intercrop was based on the consideration of reports on intercropping experiments in other countries, as well as on crops that are commonly grown in Samoa. Cabbage, yardlong bean and tomato are all important vegetable crops in Samoa. 2.2: MATERIALS AND METHODS Two trials were conducted at the University of the South Pacific, School of Agriculture and Food technology, Alafua campus, Samoa. The first trial was carried out from April to July In this trial, head cabbage (Brassica oleracea) variety racer drumhead, tomato (Lycopersicon esculentum) variety island red, and yardlong bean (Vigna unguiculata ssp. sequipedalis) were grown in various combinations. From the result of the first trial, the best intercropping combination was selected and, with some modifications, used for the second trial. The second trial was carried out from March to June : Experimental set up and treatment application Trial 1 This trial focused on study objective 1 (see section 2.1). The experimental set-up was a randomized complete block design with four treatments and five replications. The four treatments were as follows: 10

29 i. Monocrop cabbage, unsprayed with commercial insecticide. ii. Monocrop cabbage, sprayed fortnightly with commercial insecticide (Steward 150 SC, indoxacarb). iii. Two rows cabbage alternated with one row tomato, unsprayed (cabbage/tomato intercrop). iv. Two rows cabbage alternated with one row yardlong bean, unsprayed (cabbage/yardlong bean intercrop). More rows were allocated to cabbage than to either tomato/yardlong bean due to cabbage being the main crop. The alternate row arrangement was selected because of ease of application of management practices required by each crop. The sizes of individual plots were 3.5m x 1.6m and 4.2m x 1.6m for monocrop cabbage and intercropped cabbage, respectively. Adjacent plots were separated by bare earth measuring 1.5m and plant spacing was 70cm x 40cm in all treatments. Steward 150 SC (indoxacarb) insecticide was applied at the rate of 0.5ml to 1 liter of water (label rate). Steward was sprayed directly onto cabbage plants using a knapsack sprayer. Plants were sprayed until run-off. Trial 2 This trial focused on study objectives 2 and 3 (see section 2.1). Based on observation in Trial 1, the cabbage/yardlong bean intercrop was excluded in Trial 2. Additional experimental treatments were included for both monocrop cabbage and cabbage/tomato 11

30 intercrop. The experimental set up was a randomized complete block design with seven treatments and four replications. The treatments were as follows: 1. Monocrop cabbage, unsprayed with insecticide (monocrop, unsprayed). 2. Monocrop cabbage, sprayed weekly with Steward 150 SC (monocrop, sprayed weekly). 3. Monocrop cabbage, sprayed fortnightly with Steward 150 SC (monocrop, sprayed fortnigthly). 4. Two rows cabbage alternated with one row tomato, unsprayed (intercrop 2:1, unsprayed). 5. One row cabbage alternated with one row tomato, unsprayed (intercrop 1:1, unsprayed). 6. One row cabbage alternated with one row tomato, sprayed weekly (intercrop 1:1, sprayed weekly). 7. One row cabbage alternated with one row tomato, sprayed fortnightly (intercrop 1:1, sprayed fortnightly). Because of high incidence of damage observed in the two rows of cabbage and one row of tomato or yardlong bean in Trial 1, one row of cabbage and one row of tomato intercrop was introduced in Trial 2 inorder to determine the effect of tomato on insects. The size of individual plots was 2.8m x 2.1m for monocrops (treatments 1, 2 and 3) which gave 30 cabbage plants; treatment 4 plot size was 4.2m x 1.6m, which gave 20 cabbage plants and 15 tomato plants, and treatments 5, 6 and 7 were 2.8m x 2.8m, which gave 16 cabbage plants and 24 tomato plants. The varying plot size was necessary to 12

31 allow the same sample size for cabbages in all treatments. The spacing between plots was 1.5m and plant spacing was 70cm x 40cm in all treatments. In sprayed treatments, Steward 150 SC insecticide was applied to cabbage until run-off at a dilution rate of 0.5ml steward to 1 liter of water (label rate) : Agronomic practices (Trials 1 and 2) Tomato was sown in nurseries one week before head cabbage. When tomato seedlings were about 4 weeks old, they were transplanted out into the field. Cabbage seedlings were transplanted two weeks later. In treatments with yardlong bean (Trial 1), bean seeds were sown directly to field plots on the same day that tomato seedlings were transplanted. NPK (12:12:17) fertilizer was applied in all treatments at planting time at the rate of 200kg/ha. During growth, urea was applied at 100kg/ha in split applications of 10kg/ha every week for 10 weeks. Watering and weeding were done as required. Slug bait was applied around plots as necessary, to control slug and snail damage during the course of the experiment : Data collection Observations started when the cabbage plants were two weeks old in the field. Twelve cabbage plants located in the middle of each plot were observed for data collection as follows: Incidence of damage by leaf-eating caterpillars (monitored weekly). Incidence of infestation by each species of caterpillar (number of plants infested with larvae per plot) monitored weekly. Severity of damage by caterpillars (at harvest). 13

32 Number of cabbage heads produced (at harvest). Total weight of cabbage heads (at harvest). Number of marketable heads produced (at harvest). Severity of damage by caterpillars was assessed by scoring the level of damage to cabbage heads based on the following rating scale (devised by this researcher): 1 = No damage. 2 = Light damage on the old leaves, marketable. 3 = Moderate damage, several outer wrapper leaves must be removed; 1 restricted marketability. 4 = Heavy damage on cabbage head so that many wrapper leaves have to be removed leading to very small heads, or no head due to caterpillar damage : Statistical methods Data were analyzed using Genstat 5 statistical package version 4.2 (Genstat 5 Committee 2000). Because of non-normality of the data for incidence (%) of damage and incidence (%) of infestation, the data were transformed to the arcsine square root proportion + 1 scale. The transformed data were used to determine the significance of differences among the treatments (at P=0.05). Friedman test was used to analyse the severity of damage data because the raw data did not follow the normal distribution and variances were significant. Friedman test is a non-parametric equivalent of ANOVA for randomized complete block design (RCBD). Sum of ranks was used to compare the effectiveness of the different treatments. 1 Cabbage heads that were 10 cm or slightly more in diameter were included in the restricted marketability category based on observation of cabbages sold at the local markets. 14

33 2.3: RESULTS 2.3.1: Incidence of damage by leaf-eating caterpillars Trial 1 Results obtained (Figure 2.1a) show that incidence of damage by caterpillars in Trial 1 was numerically lower in cabbage/tomato and cabbage/yardlong bean treatments compared to unsprayed cabbage monocrop. Also, cabbage/tomato intercrop recorded lower incidence of damage than cabbage/yardlong bean almost throughout the duration of the experiment. However, the differences observed between the unsprayed monocrop and the intercrops were generally not statistically significant (at P=0.05) except at week 11 (refer to Appendix 1.1a). Comparing the fortnightly sprayed monocrop cabbage with the intercrops, the sprayed cabbage sustained lower incidences of damage than the intercrop during most of the experimental period. However, these differences were significant only at week 11 (refer to Appendix 1.1a). 15

34 Figure 2.1a: Incidence of damage by leaf-eating caterpillars in different cropping patterns - Trial Incidence of damage (%) Monocrop unsprayed Monocrop sprayed fortnightly Cabbage/tomato intercrop Cabbage/yardlong bean intercrop Weeks after transplanting Trial 2 Figure 2.1b shows the incidence of damage caused by leaf-eating caterpillars in the various treatments. Comparing the unsprayed cabbage monocrop with the unsprayed cabbage/tomato intercrops, the intercrops tended to record lower incidences of damage. A similar trend was observed in Trial 1. Incidences were significantly lower (at P=0.05) in the 1 row cabbage/1 row tomato intercrop (intercrop 1:1) than in the unsprayed monocrop up to 5 weeks after transplanting (refer to Appendix 1.1b). However, all unsprayed treatments (monocrop or intercrop) had 100 % incidence of damage at harvest (week 10) (Figure 2.1b). 16

35 Comparing sprayed monocrop cabbage with sprayed intercrop treatments, it was observed that sprayed intercrops numerically sustained lower incidences of caterpillar damage than monocrops with corresponding spraying frequency. This observation suggests that intercropping improved the efficiency of control in sprayed treatments. Comparing incidences in the sprayed treatments, they were lower with the weekly sprays than the fortnightly sprays. This was expected. The weekly sprayed 1 row cabbage/1 row tomato intercrop numerically sustained the lowest incidence of damage of all treatments (including weekly sprayed monocrop cabbage) from week 4 after transplanting until harvest. However, whereas all sprayed treatments were better (in terms of reducing incidence of damage) than unsprayed ones, the fortnightly sprayed treatments (monocrop or intercrop) still recorded high incidences of damage (60% - 79%) at harvest (i.e. week 10). This is in contrast to the weekly sprayed monocrop and weekly sprayed intercrop, which recorded 20% and 6% incidence of infestation, respectively at harvest (Figure 2.1b). 17

36 Figure 2.1b: Incidence of damage by leaf-eating caterpillars in different cropping system - Trial Incidence of damage (%) Monocrop unsprayed Monocrop sprayed weekly Monocrop sprayed fortnightly Intercrop 2:1 unsprayed Intercrop 1:1 unsprayed Intercrop 1:1 sprayed weekly Intercrop 1:1 sprayed fortnightly Weeks after transplanting Result summary: Incidence of damage - Intercropping either tomato or yardlong bean with cabbage tended to result in lower incidence than unsprayed monocrop cabbage (Trials 1 and 2). - Cabbage/tomato intercrop resulted in lower incidence than cabbage/yardlong bean intercrop (Trial 1). - 1 row cabbage/1 row tomato intercrop, combined with weekly application of insecticide, resulted in lower incidence of damage than weekly sprayed monocrop cabbage (Trial 2). - Incidence of damage at harvest was lower in weekly sprayed 1 row cabbage/1 row tomato intercrop (6%), followed by weekly sprayed monocrop (20%), fortnightly 18

37 sprayed 1 row cabbage/1 row tomato intercrop (60%), and then fortnightly sprayed monocrop (79%) (Trial 2). - All unsprayed treatments (monocrop and intercrop) sustained 100% incidence of damage at harvest in Trial : Incidence of infestation by each species of caterpillar : Incidence of infestation by Crocidolomia pavonana Trial 1 Figure 2.2a shows that, numerically, incidence of infestation of cabbage by C. pavonana in the intercrops was similar to, or slightly lower than the unsprayed cabbage monocrop. Significantly lower incidence (at P=0.05) than the unsprayed monocrop was only observed during week 6 in the cabbage/tomato intercrop (refer to Appendix 1.2a). Comparing intercrop treatments, cabbage/tomato intercrop had lower incidence of infestation compared to cabbage/yardlong bean intercrop during most of the observation period. However, the differences were not significant (at P=0.05) (refer to Appendix 1.2a). Incidence of infestation in the sprayed cabbage monocrop was lower than in all other treatments during most of the experimental period, but significant differences were only observed between it and the cabbage/tomato intercrop at week 6 and 10 weeks after transplanting (Figure 2.2a)(refer to Appendix 1.2a). 19

38 C. pavonana was present in the crop from week 4 until harvest in this experiment. 80 Figure 2.2a: Incidence of infestation by Crocidolomia pavonana - Trial 1. Incidence of infestation (%) Monocrop unsprayed Monocrop sprayed fortnightly Cabbage/tomato intercrop Cabbage/yardlong bean intercrop Weeks after transplanting Trial 2 The trend of infestation of cabbage by C. pavonana in Trial 2 was the same as that observed in Trial 1 numerically, lower incidence in unsprayed intercrops than in unsprayed monocrops, as well as in sprayed intercrops than in sprayed monocrops (Figure 2.2b). However, only one row cabbage/1 row tomato intercrop, unsprayed, had significantly lower incidence of infestation (at P=0.05) than the unsprayed cabbage monocrop during week 2 and weeks 4 to 7 (refer to Appendix 1.2b). 20

39 Fortnightly sprayed 1 row cabbage/1 row tomato intercrop recorded significantly (at P=0.05) lower incidence of C. pavonana infestation than unsprayed monocrop cabbage (Figure 2.2b) almost throughout the duration of the experiment (refer to Appendix 1.2b). Figure 2.2b: Incidence of infestation by Crocidolomia pavonana - Trial 2. Incidence of infestation (%) Monocrop unsprayed Monocrop sprayed weekly Monocrop sprayed fortnightly Intercrop 2:1 unsprayed Intercrop 1:1 unsprayed Intercrop 1:1 sprayed weekly Weeks after transplanting Intercrop 1:1 sprayed fortnightly Result summary: Incidence of infestation by C. pavonana - Observations in Trials 1 and 2 suggest that intercropping tended to reduce the incidence of C. pavonana infestation compared to monocropped unsprayed cabbage. - In Trial 1, numerically, cabbage/tomato intercrop had lower incidence of infestation than cabbage/yardlong bean intercrop. 21

40 - Sprayed cabbage/tomato intercrop, resulted in numerically lower incidence of infestation than monocrop cabbage sprayed at the same frequency (Trial 2). - Fortnightly sprayed 1 row cabbage/1 row tomato intercrop recorded significantly lower incidence of C. pavonana infestation than unsprayed monocrop cabbage during most of the duration of Trial 2. - C. pavonana infested the cabbage throughout the season. Peak incidences of infestation were 46.7% and 75% in Trials 1 and 2, respectively. The above observations indicate that, Numerically, intercropping reduced incidence of C. pavonana infestation in cabbage, and combining intercropping with insecticide application resulted in lower incidence of infestation than use of insecticide alone (applied at the same rate and frequency) in cabbage monocrop : Incidence of infestation by Hellula undalis Trial 1 Figure 2.3a shows the incidence of H. undalis infestation in the different cropping systems in Trial 1. Numerically, incidence of infestation tended to be lower in the unsprayed intercrops than in the unsprayed monocrop, but the differences were significant (at P=0.05) only at week 4 (refer to Appendix 1.3a). 22

41 Figure 2.3a: Incidence of infestation by Hellula undalis - Trial Incidence of infestation (%) Monocrop unsprayed Monocrop sprayed fortnightly Cabbage/tom ato intercrop Cabbage/yar dlong bean intercrop Weeks after transplanting Although incidence of infestation tended to be lower in the sprayed cabbage monocrop than in all other treatments, they were not significantly lower than the unsprayed intercrops (refer to Appendix 1.3a). Comparing the intercrop treatments, cabbage/tomato intercrop had lower incidence of infestation than cabbage/yardlong bean intercrop, although these differences were not significant (at P=0.05) (refer to Appendix 1.3a). H. undalis attack started soon after transplanting but did not continue beyond week 6 after transplanting. Incidence of infestation peaked in week 4 at 26.7%, and was much lower (below 5%) during other weeks of the experiment. Numerically, peak incidence of 23

42 infestation by this species in Trial 1 was lower in all treatments than peak incidence of infestation by C. pavonana in the same treatments (Figure 2.2a). Trial 2 Figure 2.3b shows the incidence of infestation by H. undalis in Trial 2. Numerically intercrops (unsprayed or sprayed) recorded lower incidence of infestation during peak infestation by the species (2 3 weeks after transplanting) than unsprayed monocrop. There were significant differences (at P=0.05) among the treatments at week 2 and 3 whereby the sprayed intercrops had lower incidences than the unsprayed monocrop (refer to Appendix 1.3b). Numerically, unsprayed intercrop treatments tended to record lower incidence of infestation than unsprayed monocrop during peak infestation, but they were not significantly lower (at P=0.05) (refer to Appendix 1.3b). However, the differences (at P=0.05) were not significant between 1 row cabbage/ 1 row tomato, sprayed weekly and monocrop cabbage, sprayed weekly. Similarly, no significant difference was observed between intercrop 1 row cabbage/1 row tomato, sprayed fortnightly, and monocrop cabbage sprayed fortnightly. Similar to observations in Trial 1, H. undalis attack started soon after transplanting and continued up to 5 weeks after transplanting. Also similar to the observation in Trial 1, incidence of infestation by H. undalis was numerically lower than those by C. pavonana in Trial 2 (Figure 2.2b). 24

43 Figure 2.3b: Incidence of infestation by Hellula undalis - Trial Incidence of infestation (%) Weeks after transplanting Monocrop unsprayed Monocrop sprayed weekly Monocrop sprayed fortnightly Intercrop 2:1 unsprayed Intercrop 1:1 unsprayed Intercrop 1:1 sprayed weekly Intercrop 1:1 sprayed fortnightly Result summary: Incidence of infestation by H. undalis - Intercropped cabbage recorded lower incidence of infestation by H. undalis than unsprayed monocrop cabbage in both Trials 1 and 2. - Cabbage/tomato intercrop tended to result in lower incidence of infestation than cabbage/yardlong bean intercrop (Trial 1). - Sprayed cabbage/tomato intercrop recorded lower incidence of infestation than monocrop cabbage sprayed at the same frequency (Trial 2). - H. undalis attack started soon after transplanting, but no larvae were recorded after 6 weeks after transplanting in either Trial 1 or 2. This is unlike C. pavonana, which also appeared soon after transplanting and continued to be present even at harvest. 25

44 - Peak incidence of infestation by H. undalis (26.7% and 27.1% in Trials 1 and 2, respectively) was generally lower than that of C. pavonana for corresponding treatments in both Trials 1 and : Incidence of infestation by Spodoptera litura Figure 2.4 shows the incidence of S. litura infestation in Trial 1. Numerically, few plants were infested with S. litura larvae in all treatments, but they were present in one treatment or another almost throughout the duration of the experiment. Statistical analysis revealed no significant differences (at P=0.05) (refer to Appendix 1.4) among the treatments. S. litura was not recorded in Trial 2. Figure 2.4: Incidence of infestation by Spodoptera litura - Trial Incidence of infestation (%) Monocrop unsprayed Monocrop sprayed fortnightly Cabbage/tomato intercrop Cabbage/yardlong bean intercrop Weeks after transplanting 26

45 Result summary: Incidence of infestation by S. litura - Unsprayed monocrop cabbage recorded higher incidence of infestation by S. litura than other treatments. - Few plants were infested by S. litura in all treatments. - Peak incidence of infestation by S. litura (8%) was lower than those by C. pavonana and H. undalis (in Trial 1). - S. litura was not recorded in Trial : Severity of damage to cabbage heads by leaf-eating caterpillars (at harvest) Trial 1 Numerically, intercropping treatments had lower severity of damage by caterpillars compared to unsprayed monocrop cabbage in this experiment, but the differences were not significant (at P=0.05) (Figure 2.5a) (refer to Appendix 1.5a). Comparing the intercrop treatments, cabbage/tomato intercrop had lower severity of damage than cabbage/yardlong bean intercrop, but the difference was not significant (refer to Appendix 1.5a). The fortnightly sprayed cabbage monocrop had significantly (at P=0.05) lower severity of damage than all other treatments (refer to Appendix 1.5a). 27

46 Figure 2.5a: Severity of damage to cabbage heads by leaf-eating caterpillars at harvest - Trial Severity of damage scores (1-4) Monocrop unsprayed Monocrop sprayed fortnightly Intercrop cabbage/tomato Intercrop cabbage/yardlong bean Trial 2 The observation in Trial 1, whereby unsprayed cabbage/tomato intercrop resulted in numerically lower severity of damage by caterpillars than unsprayed cabbage monocrop, was not repeated in Trial 2 (Figure 2.5b). However, both weekly and fortnightly sprayed cabbage/tomato intercrops had significantly lower severity of damage (at P=0.05) than the unsprayed cabbage monocrop (refer to Appendix 1.5b). Severity in the fortnightly sprayed 1 row cabbage/1 row tomato was lower than in the fortnightly sprayed monocrop cabbage, but not significantly so (at P=0.05) (refer to Appendix 1.5b). A similar observation was made between weekly sprayed 1 row cabbage/1 row tomato and the weekly sprayed cabbage monocrop (Figure 2.5b). 28

47 Figure 2.5b: Severity of damage to cabbage heads by leaf-eating caterpillars at harvest - Trial Severity of damage scores (1-4) Monocrop unsprayed Monocrop sprayed weekly Monocrop sprayed fortnightly Intercrop 2:1 unsprayed Intercrop 1:1 unsprayed Intercrop 1:1 sprayed weekly Intercrop 1:1 sprayed fortnightly Result summary: Severity of damage to cabbage heads by leaf-eating caterpillars - Intercropping cabbage with tomato resulted in numerically lower severity of damage than unsprayed cabbage monocrop in Trial 1, but the trend was not repeated in Trial 2. - Weekly and fortnightly sprayed cabbage/tomato intercrop resulted in significantly (at P=0.05) lower incidence than that observed in unsprayed cabbage monocrop in Trial 2. - Sprayed intercrop tended to reduce severity compared to monocrop cabbage sprayed at the same frequency. 29

48 2.3.4: Number of cabbage heads harvested per plot Trial 1 Numerically, the intercrop treatments in Trial 1 produced more heads than the unsprayed cabbage monocrop (Figure 2.6a), but the difference was significant (at P=0.05) for cabbage/tomato intercrop only (refer to Appendix 1.6a). Comparing the intercrop treatments, cabbage/tomato intercrop produced more heads than the cabbage/yardlong bean intercrop, but the difference was not statistically significant (at P=0.05). The fortnightly sprayed cabbage monocrop produced significantly (at P=0.05) more harvested heads than each of the other three treatments (refer to Appendix 1.6a). Regardless of the differences observed among the treatments, number of heads harvested from all unsprayed treatments (monocrop or intercrop) was less than half of the possible number of heads (12 heads). Figure 2.6a: Number of cabbage heads harvested from 12 data plants/plot - Trial Number of heads Monocrop unsprayed Monocrop sprayed fortnightly Intercrop cabbage/tomato Intercrop cabbage/yardlong bean 30

49 Trial 2 Figure 2.6b shows the number of heads harvested from 12 data plants per plot in Trial 2. The observation in Trial 1, whereby unsprayed cabbage/tomato intercrop resulted in significantly higher number of heads harvested than unsprayed cabbage monocrop, was not repeated in Trial 2. Infact, no useful heads could be harvested in any unsprayed treatment (intercrop or monocrop) in Trial 2 due to severe caterpillar damage, as already shown in Figure 2.5b. However, cabbage/tomato intercrop, sprayed either weekly or fortnightly produced significantly more (at P=0.05) harvested heads compared to the unsprayed cabbage monocrop (refer to Appendix 1.6b). Figure 2.6b: Number of cabbage heads harvested from 12 data plants /plot - Trial Number of heads Monocrop unsprayed Monocrop sprayed weekly Monocrop sprayed fortnightly Intercrop 2:1 unsprayed Intercrop 1:1 unsprayed Intercrop 1:1 sprayed weekly Intercrop 1:1 sprayed fortnightly 31

50 The fortnightly sprayed 1 row cabbage/1 row tomato intercrop produced more heads than the fortnightly sprayed monocrop cabbage, but not significantly so (at P=0.05). A similar observation was made between weekly sprayed monocrop cabbage and weekly sprayed cabbage/tomato intercrop. In Trial 2, the number of heads harvested from each treatment, except the weekly sprayed cabbage monocrop and the weekly sprayed 1 row cabbage/1 row tomato intercrop, was less than half of the possible number of heads, or even nil (refer to Appendix 1.6b). Result summary: Number of cabbage heads harvested/plot - Intercrop treatments produced more cabbage heads than unsprayed cabbage monocrop in Trial 1, but this trend was not repeated in Trial 2. - Unsprayed treatments (both intercrop and monocrop) had no harvestable heads in Trial 2. - In Trial 2, sprayed 1 row cabbage/1 row tomato intercrops tended to produce more harvestable heads than cabbage monocrops, sprayed at the same frequency, but the differences were not statistically significant. - Only weekly sprayed intercrop and monocrop cabbages produced more than half of the possible number of harvestable heads in Trial : Total weight of cabbage heads harvested per plot Trial 1 Figure 2.7a shows the mean total weight of cabbage heads harvested per plot from the various treatments in Trial 1. Numerically, the intercropping treatments (both of which 32

51 were unsprayed) produced slightly higher yield compared to unsprayed cabbage monocrop, while yield from cabbage/tomato intercrop was slightly higher than that from the cabbage/yardlong bean intercrop. However, none of these differences was significant (at P=0.05), and yield produced by each of these treatments was extremely low compared to the sprayed cabbage monocrop, which produced significantly higher yield than each of them (refer to Figure 2.7a, Appendix 1.7a). Figure 2.7a: Total weight (g) of cabbage heads per plot - Trial Weight (g) Monocrop unsprayed Monocrop sprayed fortnightly Intercrop cabbage/tomato Intercrop cabbage/yardlong bean Trial 2 The observation in Trial 1, whereby unsprayed cabbage/tomato intercrop resulted in slightly higher yield than the unsprayed monocrop, was not repeated in Trial 2 (Figure 33

52 2.7b). The weekly sprayed cabbage monocrop produced significantly (at P=0.05) higher total weight than each of the other treatments, except the weekly sprayed 1 row cabbage/1 row tomato intercrop (refer to Appendix 1.7b). There was no significant difference between the fortnightly sprayed cabbage/tomato intercrop and the fortnightly sprayed cabbage monocrop, although the intercrop produced slightly higher yield. Yield from both treatments were below average (less than 50% of the possible number of heads obtained from 12 data plant). Figure 2.7b: Total weight (g) of cabbage heads harvested per plot - Trial Weight (g) Monocrop unsprayed Monocrop sprayed weekly Monocrop sprayed fortnightly Intercrop 2:1 unsprayed Intercrop 1:1 unsprayed Intercrop 1:1 sprayed weekly Intercrop 1:1 sprayed fortnightly Result summary: Total weight of cabbage heads/plot - Although the intercrop treatments produced slightly higher yield than the unsprayed cabbage monocrop in Trial 1, the yield was extremely low. 34

53 - In Trial 2, the fortnightly sprayed 1 row cabbage/1 row tomato intercrop produced numerically higher yield than the fortnightly sprayed cabbage monocrop, but even the yield from the intercrop was still below average (less than 50% of the possible number of heads obtained from 12 data plant). - Only the weekly sprayed treatments (intercrop or monocrop) yielded reasonably well in Trial : Number of marketable cabbage heads Trial 1 Figure 2.8a shows the mean number of marketable heads harvested per plot in Trial 1. Numerically, the intercropping treatments produced slightly more marketable cabbage heads than the unsprayed monocrop plots (which had no marketable heads), whereas the cabbage/tomato intercrop produced slightly more marketable heads than the cabbage/yardlong bean intercrop. However, these differences were not significant (at P=0.05) and marketable heads, even in the intercrop, were extremely few (refer to Appendix 1.8a). The fortnightly sprayed cabbage monocrop produced significantly (at P=0.05) more marketable heads compared to other treatments, but even this was less than half of the possible number of heads that would be produced if there was no pest attack. 35

54 Figure 2.8a: Mean number of marketable heads of cabbage harvested per plot - Trial 1. 8 Number of marketable heads Monocrop unsprayed Monocrop sprayed fortnightly Intercrop cabbage/tomato Intercrop cabbage/yardlong bean Trial 2 In Trial 2, all unsprayed treatments (monocrop or intercrop) produced no marketable heads (Figure 2.8b). The weekly sprayed cabbage/tomato intercrop produced more marketable heads than each of the other treatments. This difference was significant, except for the weekly sprayed cabbage monocrop, which also produced significantly more marketable heads than the unsprayed or fortnightly sprayed treatments (refer to Appendix 1.8b). 36

55 In general, the sprayed intercrops had more marketable heads than monocrop cabbage sprayed at the same frequency. However, these differences were not statistically significant (at P=0.05) (refer to Appendix 1.8b). Only the weekly sprayed cabbage/tomato intercrop and the weekly sprayed cabbage monocrop produced up to half of the total number of marketable heads possible per plot (12 heads were expected from 12 data plants if pest control practice were absolutely effective) (Figure 2.8b). Figure 2.8b: Mean number of marketable heads of cabbage harvested per plot - Trial Marketable heads Monocrop unsprayed Monocrop sprayed weekly Monocrop sprayed fortnightly Intercrop 2:1 unsprayed Intercrop 1:1 unsprayed Intercrop 1:1 sprayed weekly Intercrop 1:1 sprayed fortnightly 37

56 Result summary: Number of marketable cabbage heads/plot - Unsprayed cabbage intercrop treatments produced more marketable cabbage heads than unsprayed cabbage monocrop in Trial 1, but the trend was not repeated in Trial 2. - No marketable cabbage heads were produced by unsprayed treatments (intercrop or monocrop) in Trial 2. - Insecticide application in cabbage/tomato intercrop produced more marketable heads than monocrop cabbage sprayed at the same frequency, but the increase was not statistically significant. - Only the weekly sprayed treatments (intercrop and monocrop) produced up to half the number of possible marketable heads per plot. 2.4 DISCUSSION Results from Trials 1 and 2 on incidence of damage (Figure 2.1a and b) and incidence of infestation (Figure 2.2a and b, Figure 2.3a and b, Figure 2.4) by leaf-eating caterpillars indicated that numerically, intercropping reduced or slowed down both incidence of damage and incidence of infestation compared to cabbage monocrops that received similar treatments in terms of insecticide application. Several studies have found that intercropping can reduce infestation and damage by insect pests. According to Andow (1991), out of 209 studies involving 287 insect pest species, the population of pest insects in intercropping systems was lower in 52% of the studies and higher in only 15%, compared to monoculture systems. Various explanations have been suggested in relation to the mechanism responsible for pest suppression in intercropping systems. For instance, 38

57 physical barriers and chemical smells of non-host crops partly hide the host crop which affects the host-finding ability of the pest, thus limiting the source of food for the pest (CABI, 2000; Stoll, 2000). Also, the greater diversity of the vegetation improves the condition for the development and survival of natural enemies, thus increasing their population (CABI, 2000; Stoll, 2000). For example, many natural enemies of insect pests require a supply of nector and pollen to complete their life cycle (Dent, 1991). In Trial 1, it was observed that intercropping cabbage with tomato reduced the incidence of infestation and slowed down incidence of damage by the caterpillars on cabbage better than cabbage intercropped with yardlong bean. Reduction in infestation and damage by diamondback moth due to intercropping cabbage with tomato has also been reported by Trevor (1990). Other reports have also indicated reductions in diamondback moth infestations when cabbage was intercropped with tomato (Buranday and Raros, 1973; Sivapragasam et al., 1982; Srinivasan, 1984; Varela et al., 2003), as well as reductions in C. pavonana infestation with the same intercropping systems (Varela et al., 2003). Also, Vostrikov (1915) reported that tomato and cabbage intercrop reduced infestation by insect pests on cabbage. It has been suggested that the ability of tomato intercrops to suppress these lepidopterans is due to the release of volatile substances that interfere with host-finding ability and fecundity (Buraday and Raros, 1973; Sivapragasam et al., 1982). In spite of the generally lower incidence of damage observed in unsprayed intercropping treatments compared to unsprayed monocrop cabbage, incidence of damage to cabbage heads in the intercrops was still very high at harvest (78.3% % in Trial 1 and 100% 39

58 in Trial 2) (Figure 2.1a and 2.1b). As a result, very low yield was obtained from both the cabbage/tomato and cabbage/yardlong bean intercrops in Trial 1 (Figure 2.6a, 2.7a and 2.8a) and no yield was obtained in unsprayed cabbage/tomato intercrops in Trial 2 (Figure 2.6b, 2.7b and 2.8b). Therefore, it can be concluded that intercropping alone did not achieve successful control of the cabbage caterpillars in this present study. This observation agrees with that of Srinivasan (1984) who noted that reduction in larval incidence does not significantly increase the marketable yield of cabbage in unsprayed cabbage/tomato intercrop. Similar results were also reported by Chelliah and Srinivasan (1986), Magallona (1986), and AVRDC (1987) with respect to diamondback moth. Combining intercropping with insecticide application produced slightly better control of the lepidopterans compared to monocrop cabbage sprayed at the same frequency. Similar observations were reported by Nampala et al. (1999), who noted that combining cowpea/ sorghum intercropping with insecticide application improved pest control in cowpea. It was observed that may be intercropping helped reduce the population of caterpillars to a level that spraying could be more effective against the caterpillars compared to monocrop unsprayed plots as observed in Figure 2.2a and b, Figure 2.3a and b, and Figure 3.4. The result obtained in this study demonstrated that intercropping (tomato or yardlong bean with cabbage) alone did not provide sufficient control against the leaf-eating caterpillars when infestations were high. This indicates that at present, the use of insecticides in cabbage leaf-eating caterpillar management in Samoa is probably inevitable during periods of high infestations. However other non-chemical control 40

59 alternatives can be investigated. The observation that intercropping cabbage with tomato, with insecticide application produced relatively better control of the pests than monocrops with similar insecticide regimes probably suggests that intercropping could play a role in integrated management of this pest by reducing overall insecticide use, possibly through the use of lower dosages or through a slight increase in the number of days between applications. It was noted that severity of damage by the cabbage caterpillars in Trial 2 was generally higher than observed in Trial 1 (compare Figure 2.5a and b). This was attributed to earlier onset and higher incidence of infestation in Trial 2 than in Trial 1(compare Figure 2.2a and b and Figure 2.3a and b). The earlier infestation and higher incidence can in turn be explained by the fact that Trial 1 was planted in an area that had not had a cabbage crop for several months, whereas Trial 2 was planted near infested older crops, which served as a source of infestation. Based on this present investigation, C. pavonana infested by far more plants than H. undalis and S. litura, for each set of corresponding treatments (Figure 2.2a and b, 2.3a and b, 2.4). Similarly, infestation by H. undalis was more prevalent than by S.litura. The highest recorded incidences of infestation by the various species in the two experiments were as follows: C. pavonana: 46.7% and 70.8% in Trials 1 and 2, respectively. H. undalis: 26.7% and 27.1% in Trials 1 and 2, respectively. S. litura: 8.3% in Trial 1, not recorded in Trial 2. 41

60 Diamondback moth was not recorded in either Trial 1 or 2. This was unexpected, because Hollingsworth et al. (1984) and Anonymous (1996) have reported that this species is the most destructive insect of cabbage and other cruciferous plants in Samoa. The findings of this present study seem to suggest that diamondback moth is not always a serious problem on head cabbage in Samoa, whereas the most damaging species are C. pavonana followed by H. undalis. 42

61 CHAPTER 3 RELATIVE SUSCEPTIBILITY OF FOUR HEAD CABBAGE VARIETIES TO INFESTATION BY LEAF-EATING LEPIDOPTERANS ABSTRACT The relative susceptibility of four head cabbage varieties to lepidopteran leaf-eating pests was studied in field experiments conducted at the University of the South Pacific, School of Agriculture and Food Technology, Samoa, during 2004 and The experimental design was a 4x4 Latin Square with 4 treatments. The cabbage varieties tested were KK cross, Racer drumhead, Eureka, and Copenhagen market. Results obtained showed that Copenhagen market was the most resistant to the lepidopterans based on the incidence of infestation, but it had low yield, while KK cross was considered as the most resistant to the lepidopterans based on the incidence of damage, severity of damage and yield. However, none of the four varieties in this trial showed sufficient resistance to avoid severe damage. Nevertheless, of the four varieties tested, KK cross would be the variety to include in an integrated pest management programme against these pests in Samoa. 43

62 3.1 INTRODUCTION Head cabbages grown in Samoa are often attacked by lepidopteran pests which usually cause serious damage. The most important species are cabbage cluster caterpillar (Crocidolomia pavonana) (Anonymous, 1996; Panapa, 2003), diamondback moth (Plutella xylostella) (Hollingsworth et al., 1984; Anonymous, 1996; Panapa, 2003), taro armyworm (Spodoptera litura) (Hollingsworth et al., 1984; Anonymous, 1996) and cabbage webworm (Hellula species) (Hollingsworth et al., 1984; Panapa, 2003). To obtain a good harvest, cabbage farmers, in general, rely primarily on multiple applications of synthetic insecticides to control the caterpillars. However, it has been reported elsewhere that many of these insecticides are ineffective, because some of the caterpillars are resistant to them (Talekar and Griggs, 1986; Raju, 2005). Although there is no evidence yet that this has happenned in Samoa, continuous use of insecticides might result in the development of resistant populations. Also, concern about the risks posed by agricultural chemicals to health, environment and agro-ecosystems has generated interest in reducing chemical inputs in vegetable growing. Due to these problems, research is needed to develop new control strategies that are more environmentally sound and more sustainable. Promising approaches include the development of resistant crop cultivars (Dickson et al., 1986; Palaniswamy, 1996). Plant resistance was used as a primary method of insect pest control long before the advent of synthetic organic insecticides (Adkisson and Dyck, 1980). It is one of the most effective tools for reducing insect damage (Al Ayedh, 1997). Genetic resistance to Lepidoptera is well documented in crucifers (Pimentel, 1961; Radcliffe and Chapman, 44

63 1966; Brett and Sullivan, 1974; Ellis et al., 1986; Shelton et al., 1988). For instance, resistant plants have been identified for diamondback moth and other crucifer feeders (Pimentel, 1961; Radcliffe and Chapman, 1966; Brett and Sullivan, 1974; Dickson and Eckenrode, 1975). Even varieties of crucifer crops are reported to differ in their susceptibility to attack by lepidopterans (Capinera, 2000). In the USA, descendants of the glossy cauliflower PI are resistant to diamondback moth and other lepidopterans (Dickson and Eckenrode, 1975). In his study, Stoner (1992) found that most glossy lines of PI are more resistant to imported cabbage worm (Pieris rapae L.) and diamondback moth than lines with normal leaf waxes. In Indonesia, Gunawan (1975) studied the resistance of six head cabbage cultivars (RvE 37, Osena, Yoshine 1, Yoshine 2, KY cross, and KK cross) to diamondback moth, and reported that in general, KK cross was the least infested and RvE 37 was the most infested of the six varieties tested. In Guam, KK cross had low levels of Hellula undalis and Crocidolomia pavonana but high level of S. litura compared to other crucifers (Muniappan and Marutani, 1992). This present study was carried out to compare the susceptibility of head cabbage varieties sold for cultivation in Samoa to the lepidopteran leaf-eating pests. The specific objectives of the experiment were: To compare the incidence of damage by leaf-eating caterpillars and incidence of infestation by each species of caterpillars on KK cross, Copenhagen market, Eureka, and Racer drumhead cabbage varieties. To asses the yield of the four cabbage varieties. 45

64 3.2 MATERIALS AND METHODS This trial was conducted under open field condition at the University of the South Pacific s School of Agriculture and Food Technology, Alafua Campus, Samoa, between July and September 2004 (Season 1) and was repeated from October 2004 to March 2005 (Season 2). Four head cabbage varieties ( Racer drumhead, Eureka, Copenhagen market and KK cross ), all of which are grown in Samoa, were compared for their level of resistance to diamondback moth and other leaf-eating caterpillars Experimental set up Cabbage seedlings were raised in seedbeds and transplanted (six weeks after sowing) into individual field plots (2.25m x 2.25m) in a 4x4 Latin Square Design with four treatments. The spacing between plots was 50cm x 50cm and between plants was 45cm x 45cm. The four treatments were as follows: i) KK cross ii) Racer drumhead iii) Eureka iv) Copenhagen market Agronomic practices The seedlings were transplanted into well prepared beds. A compound fertilizer (NPK, 12:12:17) was applied at transplanting at the rate of 200 kg/ha. During growth, urea was applied at 100kg/ha in split applications at 10kg/ha every week for 10 weeks. Cultural practices such as weeding and watering were carried out as required. Snail/slug bait was 46

65 placed around the plots, as often as necessary, to control slugs and snails. Natural infestations of the lepidopteran pests were allowed to develop Data collection Sixteen central plants (designated as data plants) in each plot were observed weekly for damage and infestation by caterpillars. Incidence of damage by caterpillars (number of damaged plants per plot) regardless of species, and incidence of infestation (number of plants infested by larvae of each species per plot) were recorded beginning two weeks after transplanting until harvest. At maturity, all data plants were harvested and the varieties were compared based on mean number of heads harvested, marketable heads, total weight of heads and severity of damage by caterpillars. Severity of damage by caterpillars was assessed by scoring the level of damage to cabbage heads based on the following rating scale (devised by this researcher): 1 = No damage. 2 = Light damage on the old leaves, marketable. 3 = Moderate damage, several outer wrapper leaves must be removed; 1 restricted marketability. 4 = Heavy damage on cabbage head so that many wrapper leaves have to be removed leading to very small heads, or no head due to caterpillar damage, unmarketable. 1 Cabage heads that were about 10 cm or slightly more in diameter were included in the restricted marketability category, based on observation of cabbages sold at the local markets. 47

66 3.2.4 Statistical methods Data obtained were analyzed by analysis of variance (ANOVA) using Genstat 5 Statistical package version 4.2. Because of non-normality of the data for incidence (%) of damage and incidence (%) of infestation, these data were transformed to the arcsine square root proportion + 1 scale before analysis to determine the significance of differences among the treatments (at P=0.05). 3.3 RESULTS Incidence of damage by leaf eating caterpillars Season 1 Generally, the pattern of incidence of damage in KK cross and Copenhagen market (Appendix 2a and 2b) were similar, and lower than those in Eureka and Racer drumhead (Appendix 2c and 2d), which, in turn, were similar (Figure 3.1a). Significant differences (at P=0.05) in incidence of damage were observed between KK cross and Copenhagen market (which were statistically similar) on the one hand, and Eureka and Racer drumhead (which were statistically similar) on the other, from week 3 to week 6 after transplanting (refer to Appendix 4.1a). Numerically, Copenhagen market had the lowest incidence of damage from week 3 to 7, but from week 8 until harvest (week 11), KK cross had the lowest incidence of damage. Also numerically, Eureka had lower incidence of damage than Racer drumhead during the first seven weeks of this trial (Figure 3.1a). Incidences of damage at harvest in Season 1 were 79.7 %, 89.1%, 48

67 100% and 100% for KK cross, Copenhagen market, Eureka and Racer drumhead, respectively. 120 Figure 3.1a: Incidence of damage by leaf-eating caterpillars on four cabbage varieties - Season 1. Incidence of damage (%) KK cross Racer drumhead Eureka Copenhagen market Weeks after transplanting Season 2 A generally similar pattern was observed in Season 2, although numerically, KK cross had the lowest incidence of damage throughout this season (Figure 3.1b). Significant differences (at P=0.05) in incidence of damage were observed in week 2 to week 5 (refer to Appendix 4.1b). Incidences of damage at harvest in Season 2 were 84.4%, 93.7%, 100% and 100% for KK cross, Copenhagen market, Eureka and Racer drumhead, respectively. 49

68 Figure 3.1b: Incidence of damage by leaf-eating caterpillars on four cabbage varieties - Season Incidence of damage (%) KK cross Racer drumhead Eureka Copenhagen market Weeks after transplanting Result summary: Incidence of damage by caterpillars in the four head cabbage varieties - In general, incidence of damage in KK cross and Copenhagen market were similar, while those of Eureka and Racer drumhead were similar, in both Seasons 1 and 2. - Incidences of damage were significantly lower in KK cross and Copenhagen market on the one hand, than in Eureka and Racer drumhead on the other, during some weeks in both Seasons 1 and 2. - Incidence of damage at harvest (in both Seasons 1 and 2) was lowest in KK cross, followed by Copenhagen market, followed by Eureka and Racer drumhead, both of which recorded the same final incidences in both seasons. 50

69 Regardless of the observed differences within each season, incidence of damage at harvest (week 11) in each of the four varieties was very high (80% - 100%) Incidence of infestation by each species of caterpillar on four head cabbage varieties Incidence of infestation by Crocidolomia pavonana Seasons 1 and 2 Incidence of infestation by C. pavonana in the different cabbage varieties during Season 1 is shown in Figure 3.2a. There were significance differences (at P=0.05) among the varieties at week 10 and 11 (refer to Appendix 4.2a). Copenhagen market tended to have lower incidence of infestation than the other three varieties. At harvest, incidence of infestation by C. pavonana was lowest in KK cross and Copenhagen market, followed by Eureka and Racer drumhead. Observations in Season 2 were generally similar to those of Season 1. However, Copenhagen market had the lowest incidence of infestation by C. pavonana during most of the season (Figure 3.2b, Appendix 4.2b). Incidence of infestation at harvest was lowest in Copenhagen market, followed by KK cross, Eureka and then Racer drumhead. C. pavonana was present on all varieties throughout the season in both Seasons 1 and 2, although incidences were generally lower in Season 2. 51

70 Figure 3.2a: Incidence of infestation by Crocidolomia pavonana on four head cabbage varieties - Season 1. Incidence of infestation (%) Weeks after transplanting KK cross Racer drumhead Eureka Copenhagen market Figure 3.2b: Incidence of infestation by Crocidolomia pavonana on four head cabbage varieties - Season 2. Incidence of infestation (%) KK cross Racer drumhead Eureka Copenhagen market Weeks after transplanting 52

71 Result summary: Incidence of infestation by C. pavonana - There was no distinct pattern in varietal differences during either Season 1 or 2, although Copenhagen market tended to record lower incidences of infestation than the other varieties in both seasons. - At harvest in Season 1, incidence of infestation was numerically lower in KK cross and Copenhagen market, followed by Eureka, and the highest record was in Racer drumhead. - At harvest in Season 2, incidence of infestation by C. pavonana was lowest in Copenhagen market, followed by KK cross, and then Racer drumhead. It was highest in Eureka. - C. pavonana was present in all varieties throughout the season, in both Seasons 1 and 2. - Generally, incidence of infestation by C. pavonana was lower in Season 2 (highest record on any variety =34.4%) (Figure 3.2b) than Season 1 (62.5%) (Figure 3.2a) Incidence of infestation by Hellula undalis Seasons 1 and 2 Incidence of infestation by H. undalis in Season 1 was generally low (highest record was 3.15%) (Figure 3.3a). The species was recorded only during the first five weeks after transplanting, with peak infestations occurring during the first three weeks. It was not recorded on KK cross in this season. There was no significant difference (at P=0.05) between the varieties throughtout this season (refer to Appendix 4.3a). 53

72 Figure 3.3a: Incidence of infestation by Hellula undalis on four head cabbage varieties - Season Incidence of infestation (%) KK cross Racer drumhead Eureka Copenhagen market Weeks after transplanting In Season 2, incidence of infestation by H. undalis was higher in all varieties than was observed in Season 1, with peak incidences of 6.3%, 9.4%, 15.7% and 17.2% in Copenhagen market, KK cross, Eureka and Racer drumhead, respectively. Generally, Copenhagen market and KK cross had lower incidence of infestation than Eureka and Racer drumhead (Figure 3.3b), but none of the differences was statistically significant (at P=0.05) (refer to Appendix 4.3b). Similar to the observation in Season 1, H. undalis was present only during the first five weeks after transplanting in Season 2, with peak infestation also occurring in the first three weeks. 54

73 Figure 3.3b: Incidence of infestation by Hellula undalis on four head cabbage varieties - Season 2. Incidence of infestation (%) KK cross Racer drumhead Eureka Copenhagen market Weeks after transplanting Result summary: Incidence of infestation by H. undalis - Copenhagen market and KK cross had lower incidences of H. undalis infestation than Eureka and Racer drumhead ; this was more obvious in Season 2 than in Season 1 due to higher infestation in Season 2. - In both seasons, H. undalis was present only during the first five weeks after transplanting, with peak infestation occuring in the first three weeks Incidence of infestation by Plutella xylostella Diamondback moth was not encountered on any variety in Season 1. In Season 2, Copenhagen market tended to have the lowest incidence of infestation by this species, followed by KK cross, Racer drumhead and Eureka (Figure 3.4). These differences were not statistically significant (at P=0.05) (refer to Appendix 4.4). 55

74 Figure 3.4: Incidence of infestation by Plutella xylostella on four head cabbage varieties - Season Incidence of infestation (%) KK cross Racer drumhead Eureka Copenhagen market Weeks after transplanting Incidence of infestation by Spodoptera litura Copenhagen market and Racer drumhead tended to have higher incidences of infestation by S. litura than Eureka and KK cross during Season 1 (Figure 3.5), although these differences were not statistically significant (at P=0.05) (refer to Appendix 4.5). Infestation by S. litura was very low during Season 1. No S. litura was recorded on any variety during Season 2. Relative to the other species of leaf-eating caterpillars, S. litura had by far the lowest incidence of infestation during this investigation. 56

75 Figure 3.5: Incidence of infestation by Spodoptera litura on four head cabbage varieties - Season 1. Incidence of infestation (%) KK cross Racer drumhead Eureka Copenhagen market Weeks after transplanting Severity of damage to cabbage heads by leaf-eating caterpillars (at harvest) Generally, KK cross recorded lower severity of damage than the other three varieties in both seasons (Figure 3.6), but the differences were not significant (at P=0.05) (refer to Appendix 4.6). Copenhagen market recorded lower severity of damage than Eureka and Racer drumhead. Also, the severity of damage in all varieties was above 3 on the rating scale of 1 to 4 in all varieties (1 = No damage; 2 = light damage on the old leaves, marketable; 3 = moderate damage, several outer wrapper leaves must be removed, restricted marketability; 4 = heavy damage on cabbage head so that many wrapper leaves have to be removed leading to very small heads, or no head due to caterpillar damage, unmarketable). 57

76 Figure 3.6: Severity of damage to cabbage heads by leaf-eating caterpillars (at harvest) - Season 1 and 2. Severity of damage (scores) Season 1 Season 2 0 KK cross Racer Drumhead Eureka Copenhagen market Variety Number of cabbage heads harvested per plot Generally, only KK cross and Copenhagen market produced cabbage heads in both seasons, and KK cross produced slightly more heads than Copenhagen market (Figure 3.7). However, there were no significant differences (at P=0.05) among the varieties (refer to Appendix 4.7). Furthermore, the number of heads harvested for each variety was extremely low compared to the maximum yield (16 heads) possible per plot. 58

77 Figure 3.7: Mean number of cabbage heads harvested/plot - Seasons 1 and Number of heads Season 1 Season KK cross Racer drumhead Eureka Copenhagen market Variety Total weight of cabbage heads harvested per plot Only KK cross and Copenhagen market produced harvestable heads (Figure 3.7), and KK cross had slightly heavier heads than Copenhagen market (Figure 3.8). However these differences were not significant (at P= 0.05) (refer to Appendix 4.8). 59

78 Figure 3.8: Total weight (g) of cabbage heads/plot - Seasons 1 and 2. Weight (g) KK cross Racer drumhead Eureka Copenhagen market Variety Season 1 Season Number of marketable cabbage heads KK cross was the only variety that produced marketable cabbage heads, and even then only very few (Figure 3.9, Appendix 4.9). Most heads were destroyed by the caterpillars in all varieties. 60

79 Figure 3.9: Mean number of marketable heads harvested per plot - Seasons 1 and 2. Marketable heads Season 1 Season 2 0 KK cross Racer drumhead Eureka Copenhagen market Variety 3.4 DISCUSSION In relative terms, KK cross (Appendix 2a) was the variety of cabbage that showed more resistance to the leaf-eating caterpillars based on the overall results. It had lower incidence of damage (Figure 3.1a and 3.1b), lower severity of damage at harvest (Figure 3.6), and it produced the highest yield (Figure 3.7). KK cross was also the only variety that produced some marketable heads (Figure 3.8), and total head weight was higher than Copenhagen market, which was the only other variety from which heads were harvested (Figure 3.7). The observations on KK cross appear to be in agreement with earlier findings by Gunawan (1975), who reported that KK cross was the least infested by DBM compared to other cabbage varieties (Rve 37, Osena, Yoshine 2 and KY cross), 61

80 and by Muniappan and Marutani (1992) who found that KK cross had less incidence of Crocidolomia pavonana (F.) and Hellula undalis (F.) compared to other crucifers. It has been suggested by Dickson and Eckenrode (1973) that plant resistance may be influenced by plant vigor, plant age and environmental factors. Appendix 3 shows some of the characteristics of the cabbage varieties used in this experiment. Therefore, vigorous growth and heat resistance properties of KK cross might have contributed to make this variety better able to resist damage by these pests. As a result, it grew very fast and managed to form some heads at harvest compared to the other three varieties. Another observation was that KK cross has a firm head (Appendix 3). Therefore, it is possible that the firmness of head makes it more difficult for the first instars of the lepidopterans to tunnel or mine into the leaves as the plant gets older. The neonates (newly hatched larvae) may starve to death, desiccate, drown or be washed from leaves and become vulnerable to predators (Ivey and Johnson, 1997). As a result, fewer larvae reach their final instar stage. According to Horber (1980), older plants are less preferred by insects and more difficult to damage, and Renwick (1983) mentioned that acceptance or rejection of plant by insects depends on texture. Another property of KK cross that was observed was its quick recovery when pests such as C. pavonana and H. undalis attacked the center of the plant. Due to this ability to recover from the injury, plants affected at the early stages of growth were still able to produce some heads even though these were usually smaller than those from uninfested plants. Horber (1980) has mentioned that plants could tolerate insect damage by fast regrowth and recovery from injury. 62

81 Based on the incidence of infestation by C. pavonana (Figure 3.2a and 3.2b), H. undalis (Figure 3.3b) and diamondback moth (Figure 3.4), Copenhagen market was found to be relatively more resistant to these lepidopterans. Radcliffe and Chapman (1966) have reported that Copenhagen cabbage variety was resistant to Pieris rapae (L.) (cabbageworm) and Trichoplusia ni (Hubner) (cabbage looper) larvae compared to other commercial green cabbage varieties. Compared to the other varieties, Copenhagen market had the second lowest incidence of damage (Figure 3.1a and 3.1b) and severity of damage (Figure 3.6), and second highest head weight (Figure 3.7), but it had no marketable heads (Figure 3.8). This may be due to agronomic or climatic factors that affected the growth of this variety, resulting in the generally poor growth and small plant size. Copenhangen market prefers cool dry weather (Appendix 3), which is rarely the case in Samoa. Therefore, it is possible that due to poor growth and small size of the plants, a small amount of caterpillar infestation was able to cause more severe damage compared to a variety like KK cross that had vigorous growth. In general, none of the four cabbage varieties in this trial showed sufficient resistance to avoid economic damage had this been grown as a commercial crop. The incidence of damage at harvest was very high in all the varieties ( KK cross = 80%, Copenhagen market = 90%, Eureka = 100%, Racer drumhead = 100%). The mean marketable heads harvested per plot (out of 16 heads possible) was very low ( KK cross produced 0.5 in Season 2 and 1 in Season 1, and Copenhagen market, Eureka and Racer drumhead had no marketable heads, for both Seasons). However, according to Adkisson and Dyck (1980), low or moderate resistance can enhance the effectiveness of other 63

82 control methods in an integrated system. For example, moderate level of resistance can help reduce pest population to the point where cultural control systems can control the pest (Adkisson and Dyck, 1980). Thus, of the varieties tested in this study, KK cross would appear to be more useful for use in an integrated pest management programme against these lepidopteran pests of head cabbage in Samoa. 64

83 CHAPTER 4 EFFECTS OF SOME CRUDE AQUEOUS PLANT EXTRACTS ON THE SURVIVAL OF CROCIDOLOMIA PAVONANA (FABRICIUS) ABSTRACT Two laboratory experiments were carried out at The University of the South Pacific s Alafua Campus, Samoa, during 2005 to compare the effects of crude aqueous extracts of some plants on the survival of larvae of Crocidolomia pavonana. In the first experiment, crude aqueous extracts of African basil (Ocimum gratissimum) leaves, tomato (Lycopersicon esculentum) leaves, pawpaw (Carica papaya) leaves, African marigold (Tagetes erecta) whole plant, soursop (Annona muricata) leaves, custard apple (Annona reticulata) leaves and kava (Piper methysticum) root powder were tested at high concentrations. In the second experiment, the two best extracts from the first experiment were tested at high, medium and low concentrations. In both Experiments 1 and 2, C. pavonana larvae were introduced onto square pieces (3cm x 3cm) of head cabbage leaves (variety Racer drumhead ), which had been dipped in the various extracts and placed in Petri-dishes. Untreated cabbage squares and cabbage squares dipped in a commercial insecticide (Steward 150 SC, indoxacarb) were included as controls in both Experiments 1 and 2. The experimental design was a Randomised Complete Block Design (RCBD) with nine replications for Experiment 1 and four replications for Experiment 2. Percentage mortality among larvae was recorded at 6, 12, 24, 48, and 72 hours. Leaf area eaten by larvae in each treatment was recorded at 72 hours. At the end of 72 hours in the first experiment, it was observed that each of the extracts caused significant mortality of C. pavonana larvae (basil 51.1%, tomato 55.6%, pawpaw 46.7%, African marigold 65

84 37.8%, soursop 55.6%, custard apple 35.6% and kava 77.8 %) relative to the untreated control (0%). Similarly, leaf areas damaged by larvae in the plant extracts treatments were lower than those in the untreated control. Comparing the plant extracts, mortality at each observation was highest in the kava treatment. Leaf damage was also lowest in this treatment. Next to kava (among the extracts) was basil, although this was much less effective than the kava extract. Larval mortality in the Steward insecticide treatment was higher than those in each of the plant extracts in the experiment. Steward also sustained the lowest leaf damage. Similar to Experiment 1, kava and basil treatments also recorded higher larval mortality and lower leaf damage than the untreated control, but high and medium concentrations of kava produced higher mortality and lower leaf damage than kava at low concentration and all basil treatments. Also similar to Experiment 1, Steward insecticide performed better than the plant extracts. 66

85 4.1 INTRODUCTION Production of cabbage (Brassica oleracea capitata) in Samoa is faced with numerous constraints. One of the most important is attack by diseases and pests. The most important insect pests are cabbage cluster caterpillar (Crocidolomia pavonana) (Anonymous, 1996; Panapa, 2003), diamondback moth (Plutella xylostella) (Hollingsworth et al., 1984; Anonymous, 1996; Panapa, 2003), taro armyworm (Spodoptera litura) (Hollingsworth et al., 1984; Anonymous, 1996), and cabbage webworm (Hellula species) (Hollingsworth et al., 1984; Panapa, 2003). According to Panapa (2003), cabbage cluster caterpillar is the most damaging of the four species on head cabbages. To manage pest caterpillars in cabbage crops, farmers in Samoa rely on synthetic insecticides applied at regular intervals during plant growth. However, synthetic insecticides are known to cause toxicological and environmental problems, which include toxic residues in food, soil and water, adverse effects on non-target insects and beneficial organisms, and the development of resistant strains of insects (Schmutterer, 1985; Ninsin, 1997). In order to achieve sustainable cabbage production in Samoa, it is important to identify alternative methods and pest control products that are effective, but less detrimental to users and the environment as a whole. Ahmed and Stoll (1996) have theorized that any plant species not attacked by a specific pest could provide a biopesticide to control that pest. A browse through the literature would easily reveal that many plants have been investigated for their pest control 67

86 properties. Extracts of many plants have been reported to be effective against many economically important pests (Corbett and Pagen, 1941; Pandey, 1976; Su, 1977; Crooker, 1979; Saxena, 1992; Facknath, 1999; Owusu-Ansah et al., 2000; Akakpo et al., 2001; Obeng-Ofori, 2002). There are also claims that plant extracts are generally safer than synthetic insecticides (Bokosou and Schuhbeck, 1999). Recent estimations have placed the number of plant species that are reported to possess pest control properties at more than 1800 (Charleston, 2002). Many of these have been tested against cabbage leafeating caterpillars. For example, Derris malaccensis root extract is reported to give good control against C. pavonana, P. xylostella and S. litura (Crooker, 1979). Similarly, leaf extracts of neem (Azadirachta indica), ayapana (Avapana triplinervis) and Lantana camara are reported to give good control against C. pavonana and P. xylostella in cabbage fields (Facknath, 1999). Other positive reports include the use of extracts from neem seeds/neem seed kernels for control of P. xylostella in cabbage and other crucifers (Moncada and Sanchez 1990; Schmutterer, 1992; Facknath, 1999). Moncada and Sanchez (1990) also found that the application of water extracts of onion, garlic and pepper, or old cabbage leaves, reduced P. xylostella larval populations. Corbett and Pagden (1941) reported that nicotine extract was effective in controlling P. xylostella caterpillars. Application of tomato leaf extract to cabbage is also reported to significantly reduce oviposition by P. xylostella on treated surfaces (Gupta and Thorsteinson, 1960). Some plants that occur in Samoa have been reported to have pesticidal effects against a variety of pests, elsewhere. For instance, tomato leaf extract has been reported to affect cabbage caterpillars including diamondback moth, whereas extracts of custard apple and 68

87 soursop are reported to affect diamondback moth (Stoll, 1983; Elwell and Maas, 1995). Chauhan et al. (1987) found that custard apple, sweet sop and sugar apple seed extracts exhibited insecticidal activity against Corcyra cephalonica (Lepidoptera: Pyralidae) adults. Elwell and Maas (1995) have also reported that papaya extracts affect caterpillars, cut worm, aphids and bugs, while African marigold whole plant extract affects a variety of insects. Keita et al. (2001) reported that essential oils from sweet basil (Ocimum basilicum) and African basil (Ocimum gratissimum) had an effect on newly emerged adult beetles (Callosobruchus maculatus). Although there appears to be no reports on the effect of kava against insect pests, extracts of the plant have been reported to have antibacterial (Steinmet, 1960; Onwueme and Papademetriou, 1997) and fungistatic (Onwueme and Papademetriou, 1997) properties. Hansel (1968) observed that kava extracts prepared a day before was never attacked by bacteria, yeast or other fungi, when left overnight. And according to Xuan et al. (2005), kava has allelopathic properties against weeds. Table 4.1 shows a summary of reported pesticidal properties of basil, tomato, pawpaw, African marigold, soursop, custard apple and kava, all of which occur commonly in Samoa and which were included in the experiment in this present study. Appendix 5 shows some of the chemical components of the genera to which these plants belong. 69

88 Table 4.1: Pesticidal properties of some commonly occurring plants in Samoa. Plant Active against Pesticidal properties Active constituents African basil (Ocimum gratissimum) - Microbial (Oliver,1960; Sainsbury and Sotowara, 1971) - Antimicrobial (Oliver,1960; Sainsbury and Sofowara, 1971) - Phenols (Oliver,1960; Sainsbury and Sofowara, 1971) Tomato (Lycopersicon esculentum) - Adult beetles (Callosobruchus maculatus) (Keita et al., 2001) - Cabbage caterpillars and diamondback moth (Stoll, 1986) - Fungicidal, insecticidal and repellant (Elwell and Maas, 1995) - Insecticidal, repellent, attractant, anti-feedant, bactericidal and fungicidal (Stoll, 1986; Elwell and Maas, 1995) -Eugenol (Nakamura et al., 1991) - Essential oil (Keita et al., 2001) - Tomatidine coumaroylputrescine, diferuloylputrescine, 2- tridecanone (Buckingham, 1988) Pawpaw (Carica papaya) - Caterpillars, cutworm, aphids, bugs (Elwell and Maas, 1995) - Fungicidal, nematicidal and insecticidal (Elwell and Maas, 1995) - Gluco-alkaloid, tomatine and solanine (Duke, 1985) - Cysteine protease (papain, ficin and bromelain) (Konno et al., 2003) African marigold (Tagetes erecta) Soursop (Annona uricata) and Custard apple (Annona reticulata) Kava (Piper methysticum) - Oligophagous samia rinni, Mamestra brassicas and Spodoptera litura (Konno et al., 2003) - Insects (Elwell and Maas, 1995) - Diamondback moth (Stoll, 1986; Elwell and Maas, 1995) - Corcyra cephalonica adult (Chauhan et al.,1987) - Weeds (inhibited barnyardgrass and monochoria growth) (Xuan et al., 2005) - Bactericidal, nematicidal, repellant insecticidal and contact poison (Elwell and Maas, 1995) - Contact and stomach poision, repellant, larvicidal, insecticidal and anti-feedant (Stoll, 1986) - Allelopathic (Xuan et al., 2005) - Antibacterial and fungistatic (Steinmet, 1960; Onwueme and Papademetriou, 1997) - Hydrocyanic acid (Golob et al., 1999) - Aporphine alkaloids (Oliver-bever, 1986) - Carvone, linalool, limonene (Ekundayo, 1989) - Hydrogen cyanide (Burkill, 1985) -Alkaloids, lactones, flavokavins A, B and C (Lebot and Cabalion, 1988) 70

89 The broad aim of this present study was to determine the effects of crude aqueous extracts of some plants commonly found in Samoa on the survival of C. pavonana which is an important pest of cabbage in Samoa. The specific objectives of these experiments were as follows: To compare the effects of aqueous crude extracts of some plants on the survival of C. pavonana larvae (Experiment 1). To asses the effect of different aqueous crude extracts of plants on the level of damage to cabbage leaves by C. pavonana larvae (Experiment 1). To investigate the effects of different concentrations of kava root powder and basil leaf extracts on larval mortality of C. pavonana (Experiment 2). To asses the effects of different concentrations of kava root powder and basil leaf extracts on damage caused by C. pavonana larvae on cabbage (Experiment 2). 4.2 MATERIALS AND METHODS This study involved two sets of laboratory experiments conducted at the University of the South Pacific s School of Agriculture and Food Technology, Samoa, during It involved collecting C. pavonana egg masses from cabbage fields, rearing them to larvae and then introducing the young larvae onto head cabbage leaf pieces treated with various crude aqueous plant extracts. Incidence of larval mortality and level of feeding on the leaf pieces were compared. The first set of experiments was carried out using high concentrations of plant extracts (1 part of plant material to ½ part of water weight/volume). From the first experiment, the two best extracts were selected and tested 71

90 at high, medium (1 part plant material to 1 part water) and low (1 part plant material to 2 parts water) concentrations Rearing of C. pavonana larvae for testing plant extracts C. pavonana egg masses were collected from cabbage growing in field plots and placed in Petri-dishes to hatch. The newly hatched larvae were fed on fresh cabbage leaves until they were three days old. The three-day-old larvae were used for the leaf extract experiments Treatments Experiment 1 This experiment consisted of nine treatments as follows: 1) Untreated control (no treatment applied to cabbage leaves) 2) Steward 150 SC insecticide (indoxacarb) 3) African basil (Ocimum gratissimum L.) leaf extract 4) Tomato (Lycopersicon esculentum Mill.) leaf extract 5) Pawpaw (Carica papaya L.) leaf extract 6) African marigold (Tagetes erecta L.) whole plant extract 7) Soursop (Annona muricata L.) leaf extract 8) Custard apple (Annona reticulata L.) leaf extract 9) Kava (Piper methysticum G. Forst.) root powder extract 72

91 The treatments were prepared as follows: Treatment 1: Untreated control (Head cabbage leaves were not treated with any treatment). Treatment 2: Steward 150 SC insecticide (indoxacarb) at manufacturer s recommended dilution (0.5ml Steward in a litre of water). Treatment 3: Basil leaf extract One kilogram of fresh basil leaves were cut into very small pieces, soaked in 500ml of water and allowed to stand for 24 hours. After 24 hours, the mixture was filtered using a piece of cloth to collect the leaf extracts and a teaspoon of liquid soap was added before use (adopted from Elwell and Maas, 1995). Treatment 4: Tomato leaf extract Fresh tomato leaves (variety island red ) were cut into small pieces. One kilogram of the chopped leaves were simmered in 500ml of water to extract the green juice. The solution was left for 5 hours, filtered and a teaspoon of liquid soap was added before use (adopted from Elwell and Maas, 1995). Treatment 5: Pawpaw leaf extract Fresh pawpaw leaves were shredded into pieces. One kilogram of finely shredded leaves was added to 500ml of water and shaken vigorously. The mixture was filtered with a piece of cloth to collect the leaf extract. Two teaspoons of paraffin (kerosene) and a teaspoon of liquid soap were added to the mixture before use (adopted from Elwell and Maas, 1995). 73

92 Treatment 6: African marigold whole-plant extract Fresh African marigold leaves, roots, and flowers were crushed. One kilogram of the crushed substance was placed in 500ml of boiling water and left to soak for 24 hours. Then it was filtered with a piece of cloth to collect the extract and a teaspoon of liquid soap was added before use (adapted from Elwell and Maas, 1995). Treatment 7: Soursoap leaf extract Fresh soursoap leaves were crushed. Then 1kg of the crushed leaves was placed in 500ml of boiling water and left to soak for 24 hours. A piece of cloth was used to filter out the plant extract and a teaspoon of liquid soap was added before use. Treatment 8: Custard apple leaf extract Fresh custard apple leaves were crushed into small pieces. 1kg of the crushed leaves was placed in 500ml of boiling water and left to soak for 24 hours. The plant extract was then filtered out by means of a piece of cloth and a teaspoon of liquid soap was added before use. Treatment 9: Kava root powder extract 100g of kava root powder was placed in 50ml of water, shaken vigorously and then filtered with a piece of cloth to collect the extract and then a teaspoon of liquid soap was added before use. The choice of the above plant materials for inclusion in this experiment was based primarily on their ease of availability in Samoa. 74

93 The main objective of Experiment 1 was to compare the effects of crude aqueous extracts of the above mentioned plants on the survival of C. pavonana larvae and the level of damage caused by larvae to cabbage leaves. Experiment 2 The experiment consisted of 8 treatments as follows: Treatment 1: Untreated control (no treatment applied to cabbage leaves). Treatment 2: Steward 150 SC insecticide (indoxacarb) at manufacturer recommended dilution (0.5ml in a liter of water). Treatment 3: Fresh basil leaf extract at low concentration (100g of leaves to 200ml of water). Treatment 4: Fresh basil leaf extract at medium concentration (100g of leaves to 100ml of water). Treatment 5: Fresh basil leaf extract at high concentration (100g of leaves to 50ml of water). Treatment 6: Kava root powder extract at low concentration (100g of powder to 200ml of water). Treatment 7: Kava root powder extract at medium concentration (100g of powder to 100ml of water). Treatment 8: Kava root powder extract at high concentration (100g of powder to 50ml of water). The above treatments were prepared according to the methods described for Experiment 1. 75

94 The main aim of Experiment 2 was to evaluate the effects of the different concentrations of kava root powder and basil leaf extracts on mortality of C. pavonana larvae and damage caused on cabbage leaves Testing of plant extracts on C. pavonana larvae Both Experiment 1 and 2 were layed out in a Randomised Complete Block Design, with different periods of treatment application as replicates. Each of the nine treatments in Experiment 1 was replicated nine times and each of the eight treatments in Experiment 2 was replicated four times. For both experiments, leaves of head cabbage (3cm x 3cm) were treated by dipping into the different plant extracts or Steward 150 SC insecticide. Treated cabbage leaves were then placed separately inside Petri-dishes. Therefore, there were 9 Petri-dishes per treatment application period for Experiment 1 and 8 Petri-dishes for Experiment 2. Five three-day old C. pavonana larvae were introduced onto each piece of cabbage leaf in the Petri-dishes and observed for feeding activities and survival Collection of data Data were collected for both Experiment 1 and 2 as follows: 1.) Survival of C. pavonana larvae The numbers of live and dead larvae in each Petri-dish (out of five introduced) were counted at 6 hours, 12 hours, 24 hours, 48 hours, and at 72 hours after larvae were introduced. A larva was considered as dead if there was an absence of voluntary movement even when touched. 76

95 2.) Level of damage to cabbage leaf pieces Level of damage to leaf pieces was scored at 72 hours after the introduction of C. pavonana larvae using the following scale, which was adapted from Lim et al. (1986): a) No damage = 1 b) 5% or less (45mm² or less) leaf area damaged by larvae = 2 c) 6 to 20% (54mm² to 180mm²) leaf area damaged by larvae = 3 d) 21 to 60% (189mm² to 540mm²) leaf area damaged by larvae = 4 e) 61 to 100% (549mm² to 900mm²) leaf area damaged by larvae = 5 A 1mm graph paper was used to determine the area of leaf damaged Statistical methods Data were analysed using Minitab statistical package, version 11. Statistical method used was Friedman test because the original data did not follow the normal distribution and variances were significant. Friedman test is a non-parametric equivalent of ANOVA for Randomised Complete Block Design (RCBD). Sum of ranks was used to compare the effectiveness of the different treatments. 77

96 4.3 RESULTS Survival of C. pavonana larvae Experiment 1 Mortality of C. pavonana larvae in each treatment is shown in Figure 4.1. Friedman tests showed significant differences (at P=0.05) among the treatments. Sum of ranks (Appendix 6.1a, b, c, d and e) showed that mortality of larvae in each of the plant extracts was higher than in the untreated control (which recorded no mortality throughout the experiment), with the differences becoming very pronounced at 48 hours after larvae were introduced onto the cabbage leaf pieces. However, the highest mortality was recorded in the Steward 150 SC insecticide. Of the seven plant extracts, kava root powder resulted in the highest mortality of larvae at all observations, followed by basil and tomato which were very similar, and soursop leaf extracts, and then papaya leaf, African marigold (whole plant), and custard apple leaf extracts (see sum of ranks, Appendix 6.1a, b, c, d and e). There was a significant difference (at P=0.05) between Steward 150 SC and all the other treatments at all observation times, except for kava at 72 hours. Experiment 2 Mortality of C. pavonana larvae introduced onto cabbage leaves treated with different concentrations of basil leaf and kava root powder extracts is shown in Figure 4.2. Similar to observation in Experiment 1, mortalities in the plant extract treatments were higher than in the untreated control. Friedman tests showed significant differences (at P=0.05) 78

97 Figure 4.1: Mortality of Crocidolomia pavonana larvae exposed to cabbage leaf pieces treated with different crude aqueous extracts of plants - Experiment Control 100 Steward Mortality (%) Hours after introduction of larvae Basil leaf Tomato leaf Papaya leaf African marigold Soursop leaf Custard apple leaf Kava powder Figure 4.2: Mortality of Crocidolomia pavonana larvae exposed to cabbage leaves treated with different concentrations of crude aqueous extracts of kava root powder and basil leaves- Experment 2. Control Steward Mortality (%) Basil low concentration Basil medium concentration Basil high concentration Hours after introduction of larvae Kava low concentration Kava medium concentration Kava high concentration 79

98 among the treatments. Based on the sum of ranks (Appendix 6.2a, b, c, d and e), mortality of larvae in the plant extracts was generally highest in kava high concentration treatment, followed by kava medium concentration, basil high concentration, kava low concentration, basil medium concentration and basil low concentration treatments, in that order. There was a significant difference (at P=0.05) between Steward 150 SC insecticide and all the other treatments, at all observation times, except for kava high concentration at 24 and 72 hours and kava medium at 72 hours. The kava treatments effectively increased mortality than all basil treatments, except for kava low. There was no difference between basil high, kava low, basil medium and basil low at 6, 12, 48 and 72 hours. Generally, mortality of C. pavonana larvae decreased with decrease in each extract s concentration Level of damage to cabbage leaves Experiment 1 The amount of damage caused by C. pavonana larvae to cabbage leaves in the various treatments is shown in Figure 4.3. Friedman tests showed significant difference (at P=0.05) among the treatments. Damage level in each of the seven plant extracts was generally lower than in the untreated control, which recorded total damage (median rating of 5, on a 1 to 5 score). The least damage was recorded on leaves treated with Steward insecticide, and it was significantly different from all the other treatments. It was observed that larvae started feeding on the cabbage leaves almost immediately after they were introduced onto the untreated control, but feeding did not occur in the first 6 hours in any of the other treatments (plant extracts or Steward insecticide) (refer to Appendix 80

99 7). Kava root powder extract had the lowest level of damage among the plant extracts (median rating of 3.5), and this difference was significant (at P=0.05). Basil and tomato leaf extracts were next with scores of 4.4, followed by soursop, African marigold, papaya and custard apple extracts, with scores of 4.8 each (Figure 4.3), but all six extracts were statistically similar (at P=0.05) (see sum of ranks in Appendix 6.3a). Experiment 2 The level of leaf damage caused by C. pavonana larvae in Experiment 2 is shown in Figure 4.4. Similar to observations in Experiment 1, leaf damage was, generally, reduced by the different concentrations of kava powder and basil leaf extracts compared to untreated control. All three concentrations of kava powder extracts (high, medium, low) reduced damage to a greater extent than all concentration of basil leaf extract. Friedman tests showed significant differences (at P=0.05) between kava high concentration on the one hand and kava low, basil high, basil medium and basil low concentrations on the other (refer to Appendix 6.3b). Similarly, there was no significant difference (at P=0.05) between kava high and kava medium concentrations, and among kava low, basil high, basil medium and basil low (refer to Appendix 6.3b). However, although kava high concentration recorded only about half the level of damage in the untreated control (kava high score = 2.29, untreated control score = 5.05), damage with the kava treatment was still almost twice that of Steward insecticide (1.23 score). Generally, leaf damage decreased with increased concentration of extracts for both kava and basil. 81

100 Figure 4.3: Effects of different crude aqueous extracts of plants on level of damage to cabbage leaves by Crocidolomia pavonana at 72 hours after introduction of larvae - Experiment 1. Damage level (ratings) Control Steward Basil leaf Tomato leaf Papaya leaf African marigold Soursop leaf Custard apple leaf Kava powder Treatments Figure 4.4: Effects of different concentrations of kava root powder and basil leaf extracts on damage caused to cabbage leaves by Crocidolomia pavonana at 72 hours after introduction of larvae - Experiment Damage level (ratings) Control Steward Basil low concentration Basil medium concentration Basil high concentration Kava low concentration Kava medium concentration Kava high concentration Treatments 82

101 Similar to Experiment 1, larvae did not feed on the leaves treated with plant extracts or Steward insecticide during the first six hours after they were introduced onto the leaves, but feeding started almost immediately in the untreated control (refer to Appendix 7). Result summary: Survival of C. pavonana larvae and level of damage to cabbage leaves. - C. pavonana larvae introduced onto cabbage leaves treated with crude extracts of basil leaf, tomato leaf, papaya leaf, African marigold whole plant, soursop leaf, custard apple leaf and kava root powder experienced significantly high mortality compared to the untreated control. - Mortality with kava root powder extract was higher than with the other plant extracts, and lowest in custard apple and soursop leaf extract. - When kava root extract and basil leaf extract were tested at various concentrations, mortality of larvae decreased with decreased concentration. - Level of damage to cabbage leaves treated with different plant extracts was lower than those in untreated control, although only kava had significantly lower damage than the untreated control. - Onset of feeding was delayed in the plant extract and Steward insecticide treatment but not in the untreated control. - In terms of both level of larval mortality and cabbage leaf damage, none of the plant extracts performed as well as Steward insecticide. 83

102 4.4 DISCUSSION It was observed in Experiment 1 that each of the seven plant extracts tested recorded higher mortality of C. pavonana larvae (Figure 4.1) and lower level of leaf damage (Figure 4.3) compared to untreated control which had no larval mortality at all and leaves were damaged completely by 72 hours after introduction of larvae. Similar results were also obtained in Experiment 2 (Figure 4.2 and 4.4). This probably suggests that the plant extracts contained chemicals, which caused the death of and slowed down feeding by the C. pavonana larvae. Previous reports have indicated that these plants have some chemical constituents that are active against insects, fungi, bacteria and other organisms (Table 4.1). According to Elwell and Maas (1995), basil and tomato were active against diamondback moth. Custard apple and soursop are also reported to affect diamondback moth (Stoll, 1983; Elwell and Maas, 1995). Chauhan et al. (1987) found that custard apple, sweet sop and sugar apple seed extracts exhibited insecticidal activity against Corcyra cephalonica (Lepidoptera: Pyralidae) adults. Elwell and Maas (1995) have also reported that papaya extracts affect caterpillars and cutworm. Konno et al. (2004) Pawpaw plant contains cysteine protease (papain, ficin and bromelain) in latex of the papaya tree which has effect against oligophagous Samia ricini, Mamestra brassicae and Spodoptera litura. It was observed in this present study that mortality in kava treatments was higher than those of the other treatments. There appears to be no previous report on any insecticidal properties of kava. However, Lebot and Cabalion (1988) and Lebot et al. (1992) have indicated that it has pharmacological properties. Lebot and Cabalion (1988) further reported that kava contains alkaloids. According to Golob et al. (1999), alkaloids 84

103 are secondary compounds, which give plants their anti-insect activity. Therefore, kava extract should have an effect on the C. pavonana larvae. It was observed in this experiment that the C. pavonana caterpillars did not feed on the plant extract treated leaves during the first six hours after introduction (see Appendix 7). Rather, the larvae moved as far away from the leaf pieces as possible inside the petri dishes. This was in contrast to larvae in the untreated control, which started feeding on the leaves immediately following introduction. This suggests that there was something about the extracts that repelled the larvae. This observation seems to agree with previous reports by Stoll (1986) and Elwell and Mass (1995) that basil, tomato, African marigold, custard apple and soursop have repellent properties against insects. It is also possible that death was more gradual in the plant extract treatments than Steward insecticide not only due to antifeedant properties, but also low concentration of pesticidal constituents which may have been a factor, whereby larvae needed longer periods of exposure to the extracts before mortality resulted. Regardless of the exact cause, it is noteworthy that mortality was nil or very low in the untreated control. When kava and basil were tested against C. pavonana larvae at various concentrations in Experiment 2, it was observed that reducing the concentrations resulted in reduced mortality (Figure 4.2). Therefore, it was established that high and medium concentrations of kava powder extracts caused relatively high mortality in C. pavonana larvae (Figure 4.2), which resulted in lower leaf damage (Figure 4.4) compared to basil extracts. However, basil extracts generally resulted in higher mortality and lower level of leaf 85

104 damage compared to the untreated control in which there was no larval mortality. Also, comparing kava high concentration with untreated control, kava reduced the damage level by 60%, while steward insecticide reduced damage by 80%. This indicates that kava powder extracts and basil extracts contain chemicals that cause mortality and reduce damage caused by C. pavonana larvae. There appears to be no previous report on the use of kava extracts for insect control, although there are some reports on the pharmacological and other activities of kava (see Table 4.1). Also, other members of the genus Piper to which kava belongs are reported to have anti-insect activity (Appendix 5). Although the plant extracts (basil, tomato, pawpaw, African marigold, soursop, custard apple and kava) tested in these experiments did not result in very high and rapid mortality of C. pavonana larvae compared to Steward insecticide, they did show some level of activity against the larvae. Perhaps they could be more effective on younger larvae. But considering that the extracts were prepared at high concentration before they showed the observed level of mortality, it is perhaps not beneficial to use this material in an integrated control except for high value crops. This is because of the amount of labour and cost of materials that would be involved. Furthermore, it has been reported that plant extracts deteriorate rapidly (Bokosou and Schuhbeck, 1999). This suggests that the performance of the crude aqueous extracts may be lower under field conditions. Lastly, kava root powder (whose extracts gave the best result in this experiment) is expensive and would not be worthwhile considering its level of effectiveness. 86

105 CHAPTER 5 PREDICTION OF DIAMONDBACK MOTH LARVAL INFESTATIONS OF CABBAGE BY MEANS OF PHEROMONE TRAPPING ABSTRACT A study was conducted at two locations in Samoa during 2004 to 2005, to monitor the abundance of diamondback moth (Plutella xylostella) adults and larvae. Abundance of diamondback moth adults was monitored by means of pheromone lures in delta traps mounted in or near cabbage plots, while larval infestations were monitored through visual observation of cabbage plants and counting the number of larvae present. Monitoring and data collection were done on a weekly basis. The main aim of the investigation was to determine if there was a direct relationship between the abundance of diamondback moth adults and larval infestations in a cabbage crop, and to evaluate the potential of using pheromone trapping for monitoring larval infestation in a cabbage crop. Results obtained showed that diamondback moth adult catches in pheromone traps were positively correlated with larval infestations in a crop, and pheromone trap catches can be used to predict the larval infestations. This would be less time-consuming than direct sampling and observation for larvae in the crop. However, pheromone trapping would be of limited value where other serious pests of the crop occur and would require monitoring of the crop. 87

106 5.1: INTRODUCTION Diamondback moth (DBM), Plutella xylostella (L.), has been described as the most destructive insect of head cabbage and other crucifers in Samoa (Hollingsworth et al., 1984; Anonymous, 1996) and the rest of the world (Talekar and Shelton, 1993). The method commonly used by farmers in Samoa to control this insect is synthetic insecticide, applied regularly from planting to harvesting. However, due to the ability of this insect to develop resistance to insecticides used against it (Talekar et al., 1985, 1990), it is believed that an integrated management approach is the best way of achieving sustainable management of the pest. Previous reports suggest that pheromone trapping can be used as a monitoring tool in the management of DBM. This is because some studies have shown that adult DBM catches correlated with larval populations in crops being monitored (Baker et al., 1982; Walker et al., 2003). In their study, Walker et al. (2003) found that increase in adult DBM trap catches predicted increases in larval infestations in some crucifer crops by two to three weeks in New Zealand. Baker et al. (1982) found that adult DBM catches correlated with subsequent larval populations that occurred 11 to 12 days later. In India, Reddy and Guerero (2000) reported that low population levels of DBM in pheromone traps indicated low levels of damage caused by DBM larvae. It is based on such observations that these workers have suggested that pheromone trapping could be useful as a monitoring tool in DBM management. 88

107 According to Walker et al. (2003), pheromone trap can assist in decision-making by helping farmers to identify risky periods when larval numbers in crops are likely to increase to damaging levels. This could replace the need to scout for larvae, and would be advantageous because, according to Baker et al. (1982), it is difficult to sample diamondback moth larvae in the field due to their small size and propensity to be concealed in the heart leaves. Based on their study, Reddy and Guerero (2000) concluded that pheromone is a selective and efficient tool for timing insecticide application in an IPM programme, and that an IPM programme based on pheromone trap catch threshold, natural enemies and selective use of insecticides, was more effective in reducing the level of DBM damage compared to management based solely on synthetic insecticide use. The aim of this present study was to determine whether similar observations to those reported above would be made under local field conditions in Samoa. The specific experimental objectives were as follows: To record the numbers of DBM adults caught in pheromone traps, on a weekly basis. To record the numbers of DBM larvae present in cabbage crops, also on a weekly basis. To determine the relationship between the numbers of adult DBM trap catches and larval infestation. To draw conclusions with respect to the possibility of using pheromone trap catches as a basis for prediction of DBM larval infestations and decision-making for the management of this pest in cabbage crops in Samoa. 89

108 5.2 MATERIALS AND METHODS This experiment was carried out at two locations in Upolu, Samoa, during 2004 and One location was a small commercial farm at the village of Aleisa ( S, W), where Chinese cabbage was planted in an overlapping manner all year round, in plots averaging 10m x 10m. The second location was an experimental area at Alafua ( S, W), where head cabbage was planted repeatedly nearly all year round in plots averaging 5m x 5m Pheromone trapping Commercial DBM pheromone lure capsules [containing Z11-16:Ac (cis-hexadecenyl acetate), Z11-16:Ald (cis-11-hexadecenal), and Z11-16:OH (cis-11-hexadecenol) (30:60:10)] placed on sticky bases in delta traps (Appendix 8a and b) were set up at these locations in March Two traps were mounted in or near a cabbage plot at each of the two locations. Each trap was placed about 30cm above the ground, with at least 5 meters between the traps. Lures and sticky bases were replaced every four weeks. However, the sticky base of a trap was sometimes replaced earlier if the sticky surface lost its stickiness e.g. due to being clogged with insects. At each location, traps were monitored weekly and data were recorded on the numbers of moths caught per trap. After each counting exercise, moths were removed from the sticky trap base and destroyed. The mean number of moths caught per trap per week was calculated for each site. Observations from moth trap catches and larval infestations were 90

109 compared to determine if there was a predictable trend between moth catches and larval infestation DBM larval infestation Data was also collected, concurrently, on DBM larval infestations in the cabbage plots where traps were set up. For this purpose, 30 cabbage plants were randomly selected for observation in each plot each week. Numbers of DBM larvae present on the 30 plants were determined and recorded. The total numbers of larvae counted on the 30 plants were divided by 30 to obtain the mean larvae per plant per week at each site Statistical methods The relationship between weekly larval count and pheromone trap catches was determined by correlation coefficient analysis and linear single regression. Data were analysed using Minitab statistical package version 11. Results were used to determine if there was a predictable trend between adult DBM catches and larval infestations. 5.4 RESULTS At Aleisa, DBM adult catches were relatively high from March 2004 to last week of May 2004 and again from May 2005 to June 2005, but moths were either at very low populations or absent from June 2004 to April 2005 (Figure 5.1). The highest peaks were recorded in the second week of April 2004 and last week of May 2005 indicating that peak moth activity was generally around similar period in both years. Larval infestations were relatively high in the months of March 2004 to July 2004 and again from February 91

110 2005 to June 2005, but was either very low or absent between August 2004 and mid February 2005 (Figure 5.1). Because the cabbage plots at Aleisa were grown for commercial purpose, insecticides were applied (as indicated in Figure 5.1) to control leaf-eating caterpillars. 40 Figure 5.1: Mean weekly catches of Plutella xylostella adults per pheromone trap and mean weekly counts of larvae per plant at Aleisa. 3 DBM moths/trap DBM larvae/plant DBM moths/ trap DBM larvae/ Plant Mar 5-Apr 26-Apr 17-May 7-Jun 28-Jun 19-Jul 9-Aug 30-Aug 20-Sep 11-Oct 1-Nov 22-Nov 13-Dec 3-Jan Jan 14-Feb 7-Mar 28-Mar 18-Apr 9-May 30-May 20-Jun Insecticide application Sampling Date At Alafua, there was no cabbage crop in March to last week of April 2004, therefore no DBM moths or larvae could be monitored during this period. Relatively higher adult and larval populations were recorded in January to Febuary 2005 (Figure 5.2). Outside these periods, DBM was either absent or at very low population levels. The highest peak at this 92

111 site was in the third week of January Visual comparison easily reveals that periods of DBM moth adult catches coincided with those of larval infestations (Figure 5.2). Catches of DBM moth adults and larval infestations were generally low at this site compared to Aleisa (Figure 5.1). Figure 5.2: Mean weekly catches of Plutella xylostella adults per pheromone trap and mean weekly counts of larvae per plant at Alafua DBM moths/trap DBM larvae/plant DBM moths /trap DBM larvae /Plant Mar 5-Apr 26-Apr 17-May 7-Jun 28-Jun 19-Jul 9-Aug 30-Aug 20-Sep 11-Oct 1-Nov 22-Nov 13-Dec 3-Jan 24-Jan 14-Feb 7-Mar 28-Mar Sampling Date 18-Apr 9-May 30-May 20-Jun No cabbage plants Population trends between DBM adult catches and larval infestations were basically similar between the two locations. When trap catches increased larval infestation also increased (Figure 5.1 and 5.2), although at Aleisa, application of insecticides reduced the number of larvae relative to the moths (Figure 5.1). 93

112 Correlation analysis showed significant correlation (at P=0.05) between the number of moths caught in the pheromone traps and larval infestations (refer to Appendix 9), although the relationship was stronger at Aleisa than Alafua (r = for Aleisa and r = for Alafua). Also for both locations, linear regression analysis showed significant association (P=0.05) between trap catches and larval numbers (refer to Appendix 9). The regression equation for Aleisa was Y = x and number of moths in the traps explained 79.9% of the variation in larval infestation. For Alafua, the regression equation was y = x and number of moths in the trap explained 34.4% of the variation in larval infestation. 5.5 DISCUSSION Findings from this study showed that moth trap counts and larval infestations were positively correlated, so that when number of moths caught in the pheromone traps increased, the number of larvae infesting the cabbage plants also increased (Figure 5.1 and 5.2). This positive relationship was observed for both locations. Therefore, the finding in this present study also suggests that predictions can be made on larval infestations based on moth counts in traps, to facilitate decision-making on the larval infestation and timing of insecticide application. This observation is in agreement with those of Baker et al. (1982) who found that adult catches correlated with subsequent larva populations, Walker et al. (2003) who reported that increases in moth trap catches predicted increases in larval infestations, and Reddy and Guerero (2000) who found that low population levels of DBM adults in pheromone traps indicated low levels of damage caused by DBM larvae. 94

113 Pheromone trapping appears to be a useful tool to use to forewarn of DBM larval infestation, but only if DBM alone is present, or in low population. However, when DBM catches become high as the population increases and the risk of other pests increases, then the use of normal crop scouting might be better, because scouting is required to monitor other pest infestations that might require control. For example, here in Samoa, there are other caterpillar species that may cause damage to vegetable brassicas. Therefore, pheromone trapping for diamondback moth may have limited value in such a situation. However, trap catches may be useful for monitoring DBM and help to reduce scouting time during periods when only DBM is present and is a major pest. The idea that pheromone trapping may not be a very useful monitoring tool when populations are high or when other pests that require monitoring are present has also been suggested by Walker et al. (2003). Based on this study, diamondback moth appears to be nearly present all year around in Samoa. However, results show that diamondback moth is present in higher numbers at certain times of the year than others (Figure 5.1 and 5.2). Generally higher numbers of DBM occurred during the earlier part of the year (i.e. February to April) in both years at both locations, which coincides with the wet season in Samoa (Novermber to April). Thus, at both locations, the highest abundance of DBM was in the wet season. This observation supports those of Jayarathnam (1977) and Nayarkatti and Jayanth (1982), who found that DBM population was higher during the rainy season than dry season. Ullyett (1947) and Muckenfuss et al. (1992) also reported that in their experiments, rainfall did not cause significant DBM mortality. However, the finding in this present 95

114 study contradicts those of Ooi (1986) and Sastrodiharjo (1986) who found that DBM population was higher during dry season than wet season. These authors, as well as Harcourt (1986), reported that rainfall had a direct impact on DBM larvae, but Harcourt (1963) and Sivapragasam et al. (1988) claimed that heavy rainfall only disturbed small larvae but not large ones, because large larvae are less dislodged by rain and usually regain the plant. The last point probably explains why in this present experiment, only large DBM larvae were usually found. It was also observed that the larger larvae usually fed under wrapped up leaves or inside the head of the cabbage, which probably made it difficult for rain to wash them off. Similar report was made by Muckenfuss et al. (1992) with collard plant, in which they observed that collard plants provided protection to the larvae from being dislodged by rainfall. Therefore, in terms of diamondback moth infestations at these two locations, cabbage is probably best planted in August to December when the populations are low, and assuming there are no other major pests of concern during this period. A longer trapping or other exercise would be needed before a more definite conclusion can be drawn. 96

115 CHAPTER 6 SUMMARY AND CONCLUSION Evaluation of some management strategies against lepidopteran pests of head cabbage in Samoa was conducted during 2004 and Four main investigations were conducted as follows: Effect of intercropping systems on damage by leaf-eating caterpillars and yield of cabbage (Chapter 2). Relative susceptibility of four head cabbage varieties to infestation by leaf-eating caterpillars (Chapter 3). Effect of some crude aqueous plant extracts on the survival of Crocidolomia pavonana larvae (Chapter 4). Prediction of diamondback moth larval infestations of cabbage by means of pheromone trapping (Chapter 5). i. Findings and significance of investigation reported in Chapter 2 (intercropping): Intercropping tended to reduce incidence of damage and slow down incidence of infestation by the leaf-eating caterpillars compared to unsprayed monocrop cabbage in both Trials 1 and 2. Cabbage/tomato intercrop controlled the leaf-eating caterpillars better than cabbage/yardlong bean intercrop (Trial 1). 97

116 Intercropping tended to produce more yield than unsprayed monocrop in Trial 1, but the observation was not repeated in Trial 2. Intercropping combined with insecticide application resulted in lower incidence of attack and produced slightly higher yield than monocrop cabbage sprayed at the same frequency. This study has demonstrated that intercropping cabbage with bean or tomato has some influence on the incidence of damage and infestation by the leaf-eating caterpillars. However, intercropping alone did not significantly improve cabbage yield. Combining intercropping with insecticide application resulted in a further suppression of the incidence of attack by the leaf-eating caterpillars compared to insecticide application alone. Therefore, this strategy might be useful in an integrated management programme against these pests. ii. Findings and significance of investigation reported in Chapter 3 (varietal trial): Copenhagen market had lower incidence of infestation by the leaf-eating caterpillars compared to KK cross, Eureka and Racer drumhead, but its yield was lower than KK cross. Eureka and Racer drumhead did not produce cabbage heads due to severe insect damage. KK cross had lower incidence of damage and severity of damage, and produced higher yield than the other three varieties. All four varieties sustained high levels of damage due to the caterpillars. 98

117 This study demonstrated that KK cross had more resistance to the leaf-eating caterpillars than the other three varieties tested, and appears to be the best of the four varieties for inclusion in an integrated pest management programme against these pests in Samoa. iii. Findings and significance of investigation reported in Chapter 4 (plant extracts): Each of the seven plant extracts tested recorded higher mortality of C. pavonana larvae than untreated cabbage leaves in Experiment 1. Similarly, damage to cabbage leaves was also lower with the extracts. Kava extract recorded slightly higher mortality of larvae and lower level of damage to cabbage leaves compared to other extracts in Experiment 1. Each of the different concentrations of kava and basil extracts recorded higher mortality of larvae and lower levels of damage compared to untreated cabbage leaves in Experiment 2. Kava high and medium concentrations recorded slightly higher mortality of larvae and lower levels of damage to cabbage compared to other treatments, except Steward (indoxacarb) insecticide, in Experiment 2. This study showed that crude aqueous extract of kava had some effectiveness in controlling C. pavonana in the laboratory. The highest mortality of C. pavonana and lowest level of damage was recorded with the high and medium concentrations of kava. However, the effectiveness of kava extract was much lower than the commercial insecticide (indoxacarb). Nevertheless, kava crude extract could still be investigated 99

118 further, as a possible natural pesticide for use in an integrated pest management programme. iv. Findings and significance of investigation reported in Chapter 5 (pheromone trapping): Pheromone trap catches of diamondback moth adults and larval infestations in a cabbage crop were correlated to each other at both Aleisa and Alafua experimental locations. Although not an objective of this investigation, it was observed that the population of diamondback moth was high during the wet season compared to the dry season. This study showed that there was a positive relationship between diamondback moth pheromone trap catches and diamondback moth larval infestations on cabbage. This suggests that pheromone trapping can be used to monitor larval infestations instead of physical examination of the cabbage crop. However, pheromone trapping for diamondback moth may have limited value where there are other serious pests that need to be scouted for in the same crop. It was observed in the pheromone trapping study that diamondback moth population was higher during the wet season than the dry season. Similar observations were made in the varietal susceptibility experiment and in the intercropping trials. Diamondback moth was only recorded in the wet season in the varietal susceptibility experiment, and no 100

119 diamondback moth was recorded in the intercropping trials when this experiment was carried out in the dry season. Based on the results of the above investigations, it can be generally concluded that intercropping cabbage with tomato, growing KK cross variety, and pheromone trapping could play important roles in an integrated management strategy against leaf-eating caterpillars of head cabbage in Samoa, but none of the strategies is sufficiently effective by itself. Although intercrops will effectively reduce the number of cabbage grown per unit area, it is still considered a viable or economical practice because tomato is a high value, high demand vegetable in Samoa and earnings from tomato should compensate for the slightly fewer cabbage heads grown per unit area. Also, should the cabbage crop fail, the farmer can still have a harvest from tomato crop. Moreover, cabbage cultivation in Samoa is done on small scale farms and without mechanisation, which is compatible with intercropping. The role of pheromone trapping as a monitoring tool will be relevant only if DBM is the only economical damaging species, otherwise crop scouting will be the more effective monitoring tool. It is envisaged that intercropping KK cross variety with tomato will still not provide sufficient control of the caterpillars under high infestation, therefore some insecticide use would still be necessary to achieve good yield. Based on the observation that combining intercropping with insecticide application resulted in improved control of the caterpillars (Chapter 2), it is possible that combining intercropping with slightly longer than one week interval between insecticide applications (but less than fortnightly interval, as tested 101

120 in this study), or combining intercropping with the use of a lower dilution rate of the insecticide, could still provide satisfactory control, thereby reducing overall insecticide use. However, these possibilities need to be investigated. Furthermore, insecticides must be carefully selected in order to minimize negative impacts on non-target organisms in the ecosystem. Although kava root powder extract produced the best results in terms of causing larval mortality of C. pavonana and reducing damage to cabbage leaves in Petri-dishes in the laboratory, leaf damage in this treatment was still much higher than in the commercial synthetic insecticide (indoxacarb) treatment, suggesting that the kava extract is not effective as an alternative to the synthetic insecticide. Lastly, it is important to note that there are other non-chemical pest control tools that can be investigated for inclusion in an integrated pest management system against leaf-eating caterpillars in Samoa e.g. natural enemies, trap cropping and selection of time of planting. 102

121 REFERENCES Adkisson, P.L. and Dyck, V.A. (1980). Resistant varieties in pest management systems. In Maxwell, F.G. and Jennings, P.R. (eds). Breeding plants resistance to insects. John Wiley & Sons Inc, Canada. Ahmed, S. and Stoll, G. (1996). Biopesticides. pp In: Bunders, J.B; Haverkort, B. and Hiemstra, W. (eds) Biotechnology; Building on Farmers knowledge. Macmillian Press, UK. Akakpo, A.; Obeng-Ofori, D. and Wilson, D.D. (2001). The use of biopesticides to control insect pests of papaya (Carica papaya). Journal of the Ghana Science Association 3(3): Al Ayedh, H.Y. (1997). Antixenosis: The effect of plant resistance on insect behavior. Colorado state university [Accessed: 20 February 2005] Altieri, M.A. (1999). The ecological role of biodiversity in agroecosystems. Agriculture Ecosystems and Environment 74: Andow, D.A. (1991). Vegetational diversity and arthropod population responses. Annual Review of Entomology 36: Anonymous (1930). Summary for 1930 Insect Pest Survey Bulletin X no 10. pp United States Department of Agriculture, Bureau of entomology, (In Review Applied Entomology (A) 19: 268). Anonymous (1996). Auala Tu ufa atasi mo le tausiga o toga kapisi i Samoa i sisifo. MAFFM, Samoa/SPC/GTZ. (In Samoan) Aukuso, O.; Rathman, R. and Hammans, H. (1986). Common insect pests of crops in Western Samoa. Crop protection booklet no. 1. Department of Agriculture and Forests, Apia. AVRDC (1987) progress report. Shanhua. Asia Vegetables Research and Development Center. 540pp. Baker, P.B.; Shelton, A.M and Andaloro, J.T. (1982). Monitoring of diamondback moth (Lepidoptera: Yponomeutidae) in cabbage with pheromone. Journal of Economic Entomology 75 (6): Bokosou, J. and Schuhbeck, A. (1999). How to produce home made pesticides. LAES Information Bulletin No.1/

122 Boucher, T.J. and Durgy, R. (2004). Demonstrating a perimeter trap crop approach to pest management on summer squash in New England. Journal of Extension 42(5): 1-6. Brett, C.H. and Sullivan, M.J. (1974). The use of resistant varieties and other cultural practices for control of insects on crucifers in North Carolina. North Carolina, Agriculture Experiment Station. Bulletin 449, 31pp. Brewer, G. and Ball, H.J. (1979). Effect of tamsy (Tanacetam vulgare L.) on cabbage insect s population. In: Proceedings of the North Central Branch of Entomological society of America pp. Buranday, R.P. and Raros, R.S. (1973). Effects of cabbage tomato intercropping on the incidence and oviposition of the diamondback moth, Plutella xylostella (L.). Philippine Entomology 2: Burkill, H.M (1985). The usefull plants of West Tropical Africa. Royal Botanic Garden 1, 960pp. CABI Bioscience (2000). Conservating natural enemies. Bulletin 2. 51pp. Capinera, J.L (2000). Diamondback moth, Plutella xylostella (Linn.) (Insecta: Lepidoptera: Plutellidae). Feature Creatures, University of Florida. [Accessed: 15 March 2005] Charleston, D. (2002). Hope for the humble cabbage-biological pest management programs. Bulletin of ARC Plant Protection Research Institute, Plant Protection News 60: 7 9. Chauhan, S.P.S.; Kumar, A.; Singh, C.L. and Pandey, U.K. (1987). Toxicity of some plant extracts against rice moth Corcyra cephalonica (Stainton) (Lepidoptera). Indian Journal of Entomoloy 49 (4): Chelliah, S. and Srinivasan, K. (1986). Biocology and management of diamondback moth in India. pp In: Talekar, N.T. and Griggs, T.D. (eds) Diamondback moth management. Proceeding of the First International Workshop, Tainan, Taiwan, march AVRDC Publication. Corbett, G.H. and Pagden, H.T. (1941). A review of some recent entomological investigations and observation. Malaysian Agriculture 29: Crooker, P. (1979). A home produced insecticide: Derris malaccensis. Alafua Agriculture Bulletin 4(3): Dent, D. (1991). Insect pest management. CAB International. 604pp. 104

123 Dickson, M.H and Eckenrode, C.J. (1975). Variation in Brassica oleracea resistance to cabbage looper and imported cabbageworm in the green house and field. Journal of economic entomology 68 (6): Dickson, M.H; Eckenrode, C.J. and Lin, J. (1986). Breeding for diamondback moth resistance in Brassica oleracea. pp In Talekar, N.S. and Griggs, T,D. (eds) Diamondback moth management. Proceedings of the First International Workshop, Tainan, Taiwan, March AVRDC Publication. Duke, J.A. (1985). Handbook of medicinal herbs. Florida, USA, CRC Press Inc. Ekundayo, O. (1989). A review of the volatiles of the Annonaceae. Journal of Essential Oil Research, 1(5): Ellis, P.R.; Hardman, J.A.; Thompson, A.R.; Mayne, H.J. and Saw, P.L. (1986). Resistances of vegetables to insect pests brassicas. In: 36 th Annual Report 1985, National Vegetable Research Station, Wellesbourne, U.K. 24pp. Elwell, H. and Maas, M. (1995). Natural pest and disease control. Natural Farming Network, Harare, Zimbabwe. 128 pp. Facknath, S. (1999). Control of Plutella xylostella and Crocidolomia pavonana through the combined effects of Bacillus thuringiensis and botanical pesticides. Food and Agriculture Research Council, Reduit, Mauritius. pp Freres, T. and Atalifo, K. (2000). Cabbage pests and their natural enemies in Fiji. South Pacific Commission. Fullerton, R.A. (1979). Use of the synthetic pyrethroids fenvalerate and cypermethrin to control diamondback moth (Plutella xylostella L.) and the large cabbage moth (Crocidolomia pavonana (Zeller)) in Rarotonga, Cook Is. Fiji Agricultural Journal 41 (1): Golob, P.; Moss, C.; Dalas, M.; Fidgen, A.; Evans, J and Gudrups, I. (1999). The use of spices and medicinals as bioactive protectants for grains. FAO Agriculural Services Bulletin 137: 239pp. Gunawan, B. (1975). Susceptibility of several cabbage varieties toward Plutella maculipennis Curt (= Plutella xylostella Linn) (in Indonesia). Thesis, Department of Biology, Bandung Institute of Technology, Bandung, West Java, Indonesia. 70 pp. Gupta, R.A. and Thorsteinson, A.J. (1960). Food plant relationship of diamondback moth, Plutella maculipennis (Curt.). II. Sensory relationship of oviposition of the adult female. Entomology Experimental Application 3:

124 Hansel, R. (1968). Characterization and physiological activity of some kava constituents. Pacific Science 22(3): Harcourt, D.G. (1963). Major mortality factors in population dynamics of diamondback moth, Plutella maculipennis (Curt.) (Lipdoptera: Plutellidae). Canadian Entomology Society 32: Harcourt, D.G. (1986). Population dynamics of diamondback moth in South Otario. pp In: Talekar N.S. and Griggs, T.D. (Eds) Diamondback moth management. Proceedings of the First International workshop, 11 to 15 March 1985, Tainan, Taiwan. AVRDC Publication. Hill, D.S. (1983). Agricultural Insect pests of the tropics and their control, Second edition. Cambridge University Press, Cambridge, U.K.746pp. Hollingsworth, R.G.; Matalavea, S. and Hammans, H. (1984). Insecticide experiment against pests of head cabbage in Western Samoa. Alafua Agriculture Bulletin 9 (3): Hollingsworth, R and Aloalii, I. (1985). Insect control on head cabbage. Crop Protection Leaflet No 7. Department of Agriculture, Forests and Samoa German Crop Protection Project, Apia, Samoa. 4pp. Hooks, C.R.R. and Johnson, M.W. (2002). Lepidopteran pest populations and crop yields in row intercropped broccoli. Agriculture and Forest Entomology 4 (2): Horber, E. (1980). Types and classification of resistance. pp In Maxwell, F.G. and Jennings, P.R. (eds) Breeding plants resistance to insects. John Wiley & Sons Inc, Canada. IRRI. (1974). Multiple cropping. pp In: Annual Report for International Rice Research Institute, Los Banos, Philippines. Ivey, P.W. and Johnson, S.J. (1997). Efficacy of bacillus thuringiensis and cabbage cultivar resistance to diamondback moth (Lepidoptera: Yponomeutidae). Florida Entomologist 80(3): Jayarathnam, K. (1977). Studies on the population dynamics of diamondback moth, Plutella xylostella (Linnaeus)(Lepidoptera, Yponomeutidae) and crop loss due to the pest in cabbage. Ph.D. thesis. University of Agriculture Sciences, Bangalore. 215pp. Karel, A.K.; Lakhani, D.A. and Ndunguru, B.J. (1982). Intercropping of Maize and Cowpea: Effect of plant populations on insect pests and seed yield. pp In: Keswani, C.L. and Nunguru, B.J. (Eds) Intercropping: Proceedings of the Second Symposium on Intercropping in Semi Arid Areas, held in Morogoro, Tanzania, 4 7 August International Development Research center, Ottawa, Canada. 106

125 Karungi, J.; Nampala, M.P.; Adipala, E.; Kyamanywa, S. and Ogenga-Latigo, M.W. (1999). Population dynamics of selected cowpea insect pests as influenced by different management practices in Eastern Uganda. African Crop Sciences Journal 7(4): Keita, S.M.; Vincent, C.; Schmit, J.P.; Arnason, J.T. and Belanger, A. (2001). Efficacy of essential oil of Ocimum basilicum L. and O gratisssium L. applied as an insecticide fumigant and powder to control Callosobruchus maculates (Fab.) [Coleoptera: Bruchidae]. Jouranal of Stored Products Research 37: Kessing, J.L. and Mau, R.F.L. (2007). Hellula undalis (Fabricius). Department of Entomology, University of Hawaii. [Accessed: 26 October 2007] Konno, K.; Hirayana, C.; Nakamura, M.; Tateishi, K.; Tamura, Y.; Hattori, M. and Kohno, K. (2004). Papain protects papaya trees from herbivorous insects: role of cysteine proteases in latex. Plant journal for cell and molecular biology 37: Kuma, S. (2007). Armyworm (Spodoptera litura). Fact sheet. [Accessed: 26 October 2007] Lebot, V. and Cabalion, P. (1988). Kavas of Vanuatu: Cultivars of Piper methysticum Forst. South pacific commission, Noumea, New caledonia. Technical paper 195, 191pp. Lebot, V.; Melin, M. and Lundstorm, L. (1992). Kava, the pacific drug. Yale university press, New Heavin. 255pp. Lim, G.; Sivapragasam, A. and Ruwaida, M. (1986). Impact assessment of Apanteles plutellae on diamondback moth using insecticide check method. pp In: Talekar N.S. and Griggs, T.D. (Eds) Diamondback moth management. Proceedings of the First International workshop, 11 to 15 March 1985, Tainan, Taiwan. AVRDC Publication. Maddison, P. (1984). Review of major insect pests of crop in the South Pacific. In: Course Proceedings, Sub Regional Training Course on Methods of Controlling Disease, Insects and other Pests of Plants in the South Pacific, October 4 20, 1992, Vaini, Kingdom of Tonga. MAFF, Tonga/GTZ/ USAID/CICP. 509pp. Magallona, E.D. (1986). Developments in diamondback moth in Phillipines. pp In: Talekar, N.T. and Griggs, T.D. (eds) Diamondback moth management. Proceeding of the First International Workshop, Tainan, Taiwan, march AVRDC Publication. Moncada, J.R. and Sanches, R.J. (1990). Control microbial quimico de Plutella xylostella L. enla Escuela Agricola Panamerica, Departemento Francisco, Morazan, Honduras. 107

126 Memoria del Taller International de Manejo Inte grado de Plagas en el cutivo de Repollo. El Zamorano, Honduras March Ceibra. Muckenfuss, A.E.; Shepard, B.M. and Ferrer, E.R. (1992). Natural mortality of diamondback moth in Coastal South Carolina. pp In: Talekar, N.S (ed) Diamondback moth and other crucifer Pests. Proceedings of the Second International Workshop, Tainan, Taiwan, December AVRDC Publication. Muniappan, R. and Maratani, M. (1992). Pest management for head cabbage production on Guam. pp In: Talekar, N.S. (ed) Diamondback moth and other crucifers pests. Proceeding of the Second International Workshop, Tainan, Taiwan, December AVRDC Publication. Nakamura, C.V.; Nakamura, T.U.; Bando, E.; Melo, A.F.N.; Cortez, D.A.G. and Filho, B.P.D. (1999). Antibacterial activity of Ocimum gratissimum L. essential oil. Mem Inst Oswaldo Cruz, Rio de Janeiro 94 (5): Nampala, M.P.; Ogenga-Latigo, M.W; Kyamanywa, S.; Adipala, E.; Karungi, J.; Oyobo, N.; Obuo, J.E. and Jackai, L.E.N. (1999). Intergrated management of major field pests of cowpea in Eastern Uganda. African Crop Sciences Journal 7(4): Nickel, J.L. (1973). Pest situation in changing agricultural systems: A review. Bulletin of Entomology society of America 35: Ninsin, D.K. (1997). Insecticide use patterns and residue levels on cabbage Brassica oleracea var capitata L. cultivated within the Accra Tema Metropolitan areas of Ghana. Master of Philosophy thesis, Insect Science Program, University of Ghana, Legon Accra. 85pp. Obeng-Ofori, D. and Ankrah, D.A. (2002). Effectiveness of aqueous neem extracts for the control of insect pests of cabbage (Brassica oleracea var capitata L.) in the Accra plains of Ghana. Agricultural and Food Science Journal of Ghana 1: Oliver, B. (1960). Medical plants in Nigeria. Nigerian Colloge of Arts, Science and Technology, Nigeria. 42pp. Onwueme, I.C. and Papademetriou, M.K. (1997). The kava crop and its potential. FAO, Bungkok, Thailand. Ooi, A. C. P. (1986). Diamondback moth in Malaysia. pp In: Talekar N.S. and Griggs, T.D. (Eds) Diamondback moth management. Proceedings of the First International workshop, 11 to 15 March 1985, Tainan, Taiwan. AVRDC Publication. Owusu-Ansah, F.; Afreh-Nuamah, D.; Obeng-Ofori, D. and Ofusu-Budu, K.G. (2001). Managing of infestation levels of major insect pests of garden eggs (Solanum 108

127 integrifolium L.) with agueous neem seed extracts. Journal of Ghana Science Association 3(3): 70 84). Palaniswamy, P. (1996). Host plant resistance to insect pests of cruciferous crops with special references to flea beetles feeding on canola a review. In: Dias, J.S.; Crute, I. and Monteiro, A.A. (EDS). ISHS Brassica Symposium- ix crucifer genetic 64 (1). 407pp. [Accessed: 26 October 2007] Panapa, S. (2003). Comparative effectiveness of attack, orthene and steward insecticides for the control of leaf eating caterpillars on head cabbage in Samoa. Project Report for Fulfillment of Bachelor in Agriculture, University of South Pacific, Apia, Samoa. 28pp. (Unpublished) Pandey, N.D; Singh, S.R. and Teaweri, G.C. (1976). Use of some plant powders, oils and extracts as protectants against pulse beetle, Callosobruchus chinensis Linn. Indiana Journal of entomology 38(2): Pimentel, D. (1961). An evaluation of insect resistance in broccoli, brusssels sprouts, cabbage, collards, and kale. Journal of Economic Entomology 54 (1): Radcliffe, E.B. and Chapman, R.K. (1966). Varietal resistance to insect attack in various cruciferous crops. Journal of Economic Entomology 59 (1): Raju, S.V.S. (2005). An overview of Insecticide Resistance in Plutella xylostella L. in India. Department of Entomology, Institute of Agriculture Science, Banaras Hindu University. [Accessed: 26 October 2007] Reddy, G.V.P. and Guerrero, A. (2000). Optimum timing of insecticide applications against diamondback moth Plutella xylostella in cole crops using threshold catches in sex pheromone traps. Pest Management Science 56: Renwick, J.A.A. (1983). Nonpreference mechanisms: Plant characteristics influencing insect behavior. pp In: Hedin, P.A. (ed). Plant resistance to insects. Based on the symposium sponsored by the ACS Division of Pesticide and Chemistry at the 183 rd Meeting of American Chemical Society, Las Vegas, Nevada, March 28 April 2, American Chemical Society, Washington, D.C. Rueda, A. and Shelton, T. (1995). Croci or cabbage head caterpillar (CHC). Cornell International for food, agriculture and development. [Accessed: 24 May 2004] Sainsbury, M. and Sofowora, E.A. (1971). Essential oil from the leaves and inflorescence of Ocimum gratissimum. Phytochemistry 10:

128 Sastrodiharjo, S. (1986). Diamondback moth in Indonesia. pp In: Talekar N.S. and Griggs, T.D. (Eds) Diamondback moth management. Proceedings of the First International workshop, 11 to 15 March 1985, Tainan, Taiwan. AVRDC Publication. Saxena, R.C.; Dixit, O.P. and Harshan, V. (1992). Insecticidal action of Lantana camara against Callosobruchus chinensis (Coleoptera: Bruchidae). Journal of Stored Product Research 28(4): Schmutterer, H. (1985). Which insect pests can be controlled by application of neem kernel extracts under field condition? Journal of Applied Entomology 100: Schmutterer, H. (1992). Control of diamondback moth by applications of neem extracts. pp In: Talekar, N.S (ed.) Diamondback moth and other crucifer Pests. Proceedings of the Second International Workshop, Tainan, Taiwan, December AVRDC Publication. Shelton, A.M.; Hoy, C.W.; North, R.C.; Dickson, M.H. and Barnard, J. (1988). Analysis of resistance in cabbage varieties to damage by lepidoptera and Thysanoptera. Journal of Economic Entomology 81 (2): Sivapragasam, A.; Tee, S.P. and Ruwaida, M. (1982). Effects of intercropping cabbage with tomato, incidence Plutella xylostella (L.). MPPS Newsline 6: 6-7. Sivapragasam, A.; Ito, Y. and Saito, T. (1988). Population fluctuations of the diamondback moth, Plutella xylostella (L.) on cabbage in Bacillus thuringiensis sprayed and non-sprayed plots and factors affecting within-generation survival of in mature. Research Population Ecology 30: Southon, I.W. and Buckingham, J. (1988). Dictionary of Alkaloids. Chapman and Hall, London, UK. Srinivasan, K. (1984). Visual damage thresholds for diamondback moth, Plutella xylostella (Linnaeus) and leaf webber, Crocidolomia pavonana (Zeller), on cabbage. P.h.D Thesis. University of Agriculture Sciences, Bangalore, India. 166pp. Srinivasan, K. and Krisha Moorthy, P.N. (1992). Development and Adoption of integrated pest management for major pests of cabbage using Indian mustard as a trap crop. pp In: Talekar, N.S. (ed) Diamondback Moth and other Crucifer Pests. Proceeding of the Second International Workshop, Tainan, Taiwan, December AVRDC Publication. Steinmetz, E.P. (1960). Piper methysticum (kava) famous drug plant of the South Sea Islands, Amsterdam 46pp. Stoll, G. (1986). Natural crop protection in the tropics. Agrecol; Margraf Publishers, Germany. 188pp. 110

129 Stoll,G. (2000). Natural crop protection in the tropics, letting information come to life. Margraf Vellag Publishers, Germany. 376pp. Stoner, K. (1992). Resistance and susceptibility to insect pests in glossy line of Brassica oleracea in Connecticut, USA. pp In: Talekar, N.S. (ed) Diamondback Moth and other Crucifer Pests. Proceeding of the Second International Workshop, Tainan, Taiwan, December AVRDC Publication. Su, H.C.F. (1977). Insecticide properties of black peeper to rice weevils and cowpea weevils. Journal of Economic Entomology 70(1): Taefu, V. (1977). Pests and diseases of head and chinese cabbage. Diploma in Tropical Agriculture Project Report, Submitted to the University of the South Pacific, Alafua Campus, W. Samoa 16pp. (Unpublished) Talekar, N.S.; Yang, H.C.; Lee, S.T.; Chen, B.S. and Sun, L.Y. (Compliers) (1985). Annotated Bibliography of Diamondback Moth. Shanhua, Taiwan. Asian Vegetable Research and Development Center. 469pp. Talekar, N.S. and Griggs, T.D (eds). (1986). Diamondback moth management. Proceedings of the First International Workshop, Tainan, Taiwan, March AVRDC Publication. pp. X Talekar, N.S.; Yang, J.C. and Lee, S.T. (Compilers). (1990). Annotated Bibliography of Diamondback Moth volume 2. Shanhua, Taiwan. Asian Vegetable Research and Development Center. 199 pp. Talekar, N.S. and Shelton, A.M. (1993). Biology, ecology and management of diamond back moth. http: [Accessed: 12 April 2004] Timbilla, J.A and Nyako, K.O. (2001). Efficacy of intercropping as a management tool for the control on insect pests of cabbage in Ghana. TROPICULTURA 19 (2): Trevor, G.F (1990). Succesful organic pest control: Enviromental friendly ways to deal with unwantd garden pests and diseases. Thorsons Publishers Ltd, Wellingborough, England. Ullyett, G.C. (1947). Mortality factors in populations of Plutella maculipennis (Curtis.) (Tineidae:Lep.) and their relation to the problem of control. Entomology Mem., Union of South Africa, Department of Agriculture and Forestry 2: Varela, A.M.; Seif, A. and Lohr, B. (2003). A guide to IPM in Brassicas as production in Eastern and Southern Africa. The international Center of Insect Physiology and Ecology (ICIPE), Nairobi, Kenya. 95pp. 111

130 Vostrikov, P. (1915). Tomatoes as insecticides. The importance of solanaceae in the control of pests of agriculture. Novotcherkossk 10: (In Russian) Walker, G.P.; Wallace, A.R.; Bush, R.; Macdonald, F.H. and Suckling, D.M. (2003). Evaluation of pheromone trapping for reduction of diamondback moth infestations in vegetable Brassicas. New Zealand Plant Protection 56: Waterhouse, D.F. and Norris, K.R. (1987). Biological control, Pacific prospects. The Australia Center for International Agricultural Research, Australia. 454pp. Waterhouse, D.F. and Norris, K.R. (1989). Biological control, Pacific prospects. Supplement 1. ACIAR Monograph No. 12, 125pp. Waterhouse, D.F. (1992). Biological control of diamondback moth in the Pacific. pp In: Talekar, N.S. (ed) Diamondback Moth and other Crucifer Pests. Proceedings of the Second International Workshop, Tainan, Taiwan, December AVRDC Publication. Xuan, T.D.; Tawata, S.; Khanh, T.D. and Chung, I.M. (2005). Decomposition of allelopathic plants in soil. Journal of Agronomy and Crop Science 70(3): Zhao, J.Z., Li, C.Y.X.; Mau, R.F.L.; Thompson, G.D.; Hertlein, M.; Andaloro, J.T.; Boykin, R. and Shelton, A.M. (2006). Monitoring of diamondback moth (Lepidoptera: Plutellidae) resistance to spinosad, indoxacarb, and emamectin benzoate. Journal of Economic Entomology 99 (1):

131 APPENDICES Appendix 1: Statistical analyis on transformed data for chapter 2 (intercropping trials). 1.1a: Incidence of damage by leaf-eating caterpillars Trial 1 Weeks Treatment Monocrop, a unsprayed Monocrop, b sprayed fornightly Cabbage/tomato b intercrop Cabbage/yardlong b bean intercrop Fpr LSD (P 0.05) Means with the same letters in each column are not significantly different at P

132 Appendix 1 (continued) 1.1b: Incidence of damage by leaf-eating caterpillars Trial 2 Weeks Treatment Monocrop 0.396a 0.684a 1.571a 1.571a 1.571a 1.571a 1.571a 1.571a 1.571a unsprayed Monocrop 0.000b 0.073bc 0.146c 0.178df 0.850b 0.463d 0.463c 0.440c 0.463c sprayed weekly Monocrop 0.000b 0.073bc 0.521bc 0.563c 0.737b 1.065b 1.065b 1.091b 1.123b sprayed fortnightly Intercrop 2: b 0.453ab 0.629b 1.073b 1.424a 1.571a 1.571a 1.571a 1.571a unsprayed Intercrop 1: b 0.309b 0.544b 1.033b 1.367a 1.498a 1.498a 1.571a 1.571a unsprayed Intercrop 1: a 0.073bc 0.073c 0.073df 0.073c 0.220c 0.220d 0.220c 0.220c sprayed weekly Intercrop 1: b 0.00c 0.204c 0.358cd 0.795b 0.849c 0.849b 0.870b 0.902b sprayed fortnightly Pfr LSD ((P 0.05) Means with the same letters in each column are not significantly different at P

133 Appendix 1 (continued) 1.2a: Incidence of infestation by Crocidolomia pavonana Trail 1 Weeks Treatment Monocrop Unsprayed Monocrop sprayed fornightly Cabbage/ tomato intercrop Cabbage/yardlong bean intercrop a a bc b b a ab a Fpr LSD (P 0.05) Means with the same letters in each column are not significantly different at P b: Incidence of infestation by Crocidolomia pavonana Trial 2 Weeks Treatment Monocrop 0.625a 0.802a 1.023a 1.032a 1.109a 1.004a 0.865a unsprayed Monocrop sprayed 0.322c 0.407c 0.352d 0.499b 0.739b 0.630b 0.531b weekly Monocrop sprayed 0.322c 0.609b 0.607c 0.974b 0.739b 0.802b 0.739a fortnightly Intercrop 2: a 0.760a 1.067a 0.940a 0.959a 1.025a 0.697ab unsprayed Intercrop 1: b 0.633ab 0.781b 1.132b 0.782b 0.823b 0.853a unsprayed Intercrop 1: c 0.377c 0.352d 0.437b 0.653b 0.555c 0.533b sprayed weekly Intercrop 1: c 0.609b 0.382d 0.746b 0.674b 0.738b 0.675ab sprayed fortnightly Pfr LSD (P 0.05) Means with the same letters in each column are not significantly different at P

134 Appendix 1 (continued) 1.3a: Incidence of infestation by Hellula undalis Trial 1 Weeks Treatment Monocrop a unsprayed Monocrop sprayed b fornightly Cabbage/tomato b intercrop Cabbage/yardlong b bean intercrop Fpr LSD (P 0.05) Means with the same letters in each column are not significantly different at P b: Incidence of infestation by Hellula undalis Trial 2 Weeks Treatment Monocrop unsprayed 0.613a 0.647a Monocrop sprayed 0.322b 0.460b weekly Monocrop sprayed 0.322b 0.352b fortnightly Intercrop 2: a 0.498a unsprayed Intercrop 1: a 0.555a unsprayed Intercrop 1:1 sprayed 0.322b 0.407b weekly Intercrop 1:1 sprayed 0.322b 0.352b fortnightly Pfr LSD (P 0.05) Means with the same letters in each column are not significantly different at P

135 Appendix 1 (continued) 1.4: Incidence of infestation by Spodoptera litura Trial 1 Weeks Treatment Monocrop unsprayed Monocrop sprayed fornightly Cabbage/tomato intercrop Cabbage/yardlong bean intercrop Fpr LSD (P 0.05)

136 Appendix 1 (continued) 1.5a: Severity of damage to cabbage heads by leaf-eating caterpillars (at harvest) Trial 1 Friedman test for Severity by Treat1 blocked by Rep1 S = DF = 3 P = S = DF = 3 P = (adjusted for ties) Est Sum of Treat1 N Median Ranks Grand median = b: Severity of damage to cabbage heads by leaf-eating caterpillars (at harvest) Trial 2 Friedman test for Severity by Treat2 blocked by Rep2 S = DF = 6 P = S = DF = 6 P = (adjusted for ties) Est Sum of Treat2 N Median Ranks Grand median =

137 Appendix 1 (continued) 1.6a: Number of cabbage heads harvested per plot Trial 1 Treatment No. of cabbage head harvested/plot Monocrop, unsprayed 0.40a Monocrop, sprayed fornightly 7.40c Cabbage/tomato intercrop 3.80b Cabbage/yardlong bean intercrop 1.60ab Fpr LSD (P 0.05) Means with the same letters in each column are not significantly different at P b: Number of cabbage heads harvested per plot Trial 2 Treatment No. of cabbage heads harvested/plot Monocrop, unsprayed 0.00a Monocrop, sprayed weekly 9.50c Monocrop, sprayed fortnightly 2.50b Intercrop 2:1,unsprayed 0.00a Intercrop 1:1, unsprayed 0.00a Intercrop 1:1, sprayed weekly 11.25c Intercrop 1:1, sprayed fortnightly 4.50b Pfr LSD (P 0.05) Means with the same letters in each column are not significantly different at P

138 Appendix 1 (continued) 1.7a: Total weight of cabbage harvested per plot Trial 1 Treatment Weight of cabbage harvested/plot Monocrop, unsprayed 60a Monocrop, sprayed fornightly 5900b Cabbage/tomato intercrop 1040a Cabbage/yardlong bean intercrop 480a Fpr LSD (P 0.05) Means with the same letters in each column are not significantly different at P b: Total weight of cabbage harvested per plot Trial 2 Treatment Weight of cabbage harvested/plot Monocrop, unsprayed 0.00a Monocrop, sprayed weekly 7724c Monocrop, sprayed fortnightly 3250b Intercrop 2:1,unsprayed 0.00a Intercrop 1:1, unsprayed 0.00a Intercrop 1:1, sprayed weekly 7494c Intercrop 1:1, sprayed fortnightly 3175b Pfr LSD (P 0.05) Means with the same letters in each column are not significantly different at P

139 Appendix 1 (continued) 1.8a: Number of marketable cabbage heads harvested per plot Trial 1 Treatment Marketable cabbage harvested/plot Monocrop, unsprayed 0.00a Monocrop, sprayed fornightly 5.80b Cabbage/tomato intercrop 0.80a Cabbage/yardlong bean intercrop 0.40a Fpr LSD (P 0.05) Means with the same letters in each column are not significantly different at P b: Number of marketable cabbage heads harvested per plot Trial 2 Treatment Weight of cabbage harvested/plot Monocrop, unsprayed 0.00a Monocrop, sprayed weekly 6.75b Monocrop, sprayed fortnightly 1.50a Intercrop 2:1,unsprayed 0.00a Intercrop 1:1, unsprayed 0.00a Intercrop 1:1, sprayed weekly 7.00b Intercrop 1:1, sprayed fortnightly 2.50a Pfr LSD (P 0.05) Means with the same letters in each column are not significantly different at P

140 Appendix 2: Field plots showing damage to the four head cabbage varieties tested in the relative susceptibility experiment. 2a: KK cross 2b: Copenhagen market 2c: Eureka 2d: Racer drumhead (Photos: Adama Ebenebe, 2005) 122

141 Appendix 3: Characteristics of the four cabbage varieties used in chapter 3 (varietial trial). Cabbage variety Characteristics Source KK cross Strong frame. Semi flat cabbage, maturity days White cabbage Technisms news from transplant, firm heads all year round. Strong resistance to heat and high humidity and can be grown in low land even during rainy season. High degree of tolerance to disease. Copenhagen market Small to medium plants with short stem Firm.head Grown during cool and dry season, not in rainy season. Yates Arthur Yates & co Ltd. 21A Richmond Road, Homebush, NSW 2140 Australia Racer drumhead Large flat head, loose, wider frame. Mature earlier. Sweet flavor. Tolerate to black rot. Eureka Firm light green heads. Early maturing hybrid for coleslaws. Disease resistance and non-bursting for up to 6 weeks. Yates Arthur Yates & co Ltd. 21A Richmond Road, Homebush, NSW 2140 Australia Yates Arthur Yates & co Ltd. 21A Richmond Road, Homebush, NSW 2140 Australia 123

142 Appendix 4: Statistical analysis on transformed data for chapter 3 (varietal trials). 4.1a: Incidence of damage by leaf eating caterpillars - Season 1 Weeks Variety Copenhagen a 0.415a 0.435a a market Racer b 0.889b 1.038b b drumhead Eureka b 0.868b 0.971b b KK cross a 0.453a 0.528a a Fpr LSD (P 0.05) Means with the same letters in each column are not significantly different at P b: Incidence of damage by leaf-eating caterpillars - Season 2 Weeks Variety Copenhagen a 0.849a 0.898a 1.048a market Racer drumhead b 0.963b 1.343b 1.332b Eureka a 0.832a 0.995a 1.114ab KK cross a 0.785a 0.849a 0.964a Fpr LSD (P 0.05) Means with the same letters in each column are not significantly different at P

143 Appendix 4 (continued) 4.2a: Incidence of infestation by Crocidolomia pavonana Season 1 Weeks Variety Copenhagen a a 0.678a market Racer a b 1.022b drumhead Eureka b b 1.003b KK cross a a 0.680a Fpr LSD (P 0.05) Means with the same letters in each column are not significantly different at P b: Incidence of infestation by Crocidolomia pavonana Season 2 Weeks Variety Copenhagen a market Racer a drumhead Eureka b KK cross a Fpr LSD (P 0.05) Means with the same letters in each column are not significantly different at P

144 Appendix 4 (continued) 4.3a: Incidence of infestation by Hellula undalis Season 1 Weeks Variety Copenhagen market Racer drumhead Eureka KK cross Fpr LSD (P 0.05) b: Incidence of infestation by Hellula undalis Season 2 Weeks Variety Copenhagen market Racer drumhead Eureka KK cross Fpr LSD (P 0.05) : Incidence of infestation by Plutella xylostella Season 2 Weeks Variety Copenhagen market Racer drumhead Eureka KK cross Fpr LSD (P 0.05)

145 Appendix 4 (continued) 4.5: Incidence of infestation by Spodoptera litura Season 1 Weeks Variety Copenhagen market Racer drumhead Eureka KK cross Fpr LSD (P 0.05) : Severity of damage to cabbage heads by leaf-eating caterpillars (at harvest) Seasons 1 and 2 Variety Season 1 Season 2 Copenhagen market Racer drumhead Eureka KK cross Fpr LSD (P 0.05) : Number of cabbage heads harvested per plot Seasons 1 and 2 Variety Season 1 Season 2 Copenhagen market Racer drumhead Eureka KK cross Fpr LSD (P 0.05)

146 Appendix 4 (continued) 4.8: Total weight (g) of cabbage heads per plot Seasons 1 and 2 Variety Season 1 Season 2 Copenhagen market Racer drumhead 0 0 Eureka 0 0 KK cross Fpr LSD (P 0.05) : Number of marketable cabbage heads harvested per plot Seasons 1 and 2 Variety Season 1 Season 2 Copenhagen market Racer drumhead Eureka KK cross Fpr LSD (P 0.05)

147 Appendix 5: Toxicity data for some chemical components found in plant genera used in the plant extract experiment (adapted from Golob et al., 1999). Plant genus Chemical Toxicity Ocimum Carvacrol Cineole (1-8) Citral Esdragole (estragole) Eugenol Hydrocyacnic acid Limonene Linalool Saponin Anethole Borneol Shikimol oral LD mg oral rat LD mg oral rat LD mg oral rat LD mg oral rat LDLo 500mg oral hmn LDLo 570mg oral rat LDLo 4600mg oral rat LD mg oral mus LDLO 3000mg oral rat LD mg oral rbt LDLo 200mg Annona Hydrocyanic acid oral hmn LDLo 570mg Tagetes Hydrocyanic acid oral hmn LDLo 570mg Lycopersicon Piper Ethyl alcohol Histamine Malic acid Methanol Noscapine Oxalic acid Rutin (sophorin) Solanine Tomatine Anethole Apiole scumus Asarone Carene Cineole (1-8) Citral Eugenol Hydrocyanic Limonene Phellandrene Pipericide Shikimol oral man LDLo 50mg ivn dog LDLo 50mg oral rat LDLo 1600mg oral hmn LDLo 340mg ivn mus LD 50 83mg oral hmn LDLo 700mg ivn mus LD mg ipr mus LD 50 32mg oral rat LDLo 800mg oral rat LD mg LD mg ipr gpg LD mg oral rat LD mg oral rat LD mg oral rate LD mg oral rate LDLo 500mg oral hmn LD mg oral rat LDLo 4600mg 129

148 Appendix 6: Statistical analysis on data for chapter 4 (plant extract experiment). 6.1: Survival of C. pavonana larvae in plant extracts - Experiment 1 6.1a: Friedman test for 6 hour by treatmen blocked by Rep S = DF = 8 P = S = DF = 8 P = (adjusted for ties) Est Sum of treatmen N Median Ranks Grand median = b: Friedman test for 12 hour by treatmen blocked by Rep S = DF = 8 P = S = DF = 8 P = (adjusted for ties) Est Sum of treatmen N Median Ranks Grand median =

149 Appendix 6 (continued) 6.1c: Friedman test for 24 hour by treatmen blocked by Rep S = DF = 8 P = S = DF = 8 P = (adjusted for ties) Est Sum of treatmen N Median Ranks Grand median = d: Friedman test for 48 hour by treatmen blocked by Rep S = DF = 8 P = S = DF = 8 P = (adjusted for ties) Est Sum of treatmen N Median Ranks Grand median =

150 Appendix 6 (continued) 6.1e: Friedman test for 72 hour by treatmen blocked by Rep S = DF = 8 P = S = DF = 8 P = (adjusted for ties) Est Sum of treatmen N Median Ranks Grand median =

151 Appendix 6 (continued) 6.2: Survival of C. pavonana larvae in plant extracts - Experiment a: Friedman test for 6 hour by treatmen blocked by Rep S = DF = 7 P = S = DF = 7 P = (adjusted for ties) Est Sum of treatmen N Median Ranks Grand median = b: Friedman test for 12 hour by treatmen blocked by Rep S = DF = 7 P = S = DF = 7 P = (adjusted for ties) Est Sum of Treatmen N Median Ranks Grand median =

152 Appendix 6 (continued) 6.2c: Friedman test for 24 hour by treatmen blocked by Rep S = DF = 7 P = S = DF = 7 P = (adjusted for ties) Est Sum of treatmen N Median Ranks Grand median = d: Friedman test for 48 hour by treatmen blocked by Rep S = DF = 7 P = S = DF = 7 P = (adjusted for ties) Est Sum of treatmen N Median Ranks Grand median =

153 Appendix 6 (continued) 6.2e: Friedman test for 72 hour by treatmen blocked by Rep S = DF = 7 P = S = DF = 7 P = (adjusted for ties) Est Sum of Treatmen N Median Ranks Grand median =

154 Appendix 6 (continued) 6.3: Level of damage to cabbage leaves by C. pavonana larvae in plant extracts. 6.3a: Friedman test for Damage 1 by treatmen blocked by Rep Experiment 1 S = DF = 8 P = S = DF = 8 P = (adjusted for ties) Est Sum of treatmen N Median Ranks Grand median = b: Friedman test for Damage 1 by treatmen blocked by Rep Experiment 2 S = DF = 7 P = S = DF = 7 P = (adjusted for ties) Est Sum of treatmen N Median Ranks Grand median =

155 Appendix 7: Pictures showing the effects of different treatments on C. pavonana larval feeding activities at 6 hours (plant extract experiment). Larva Larva Steward (insecticide) Control (untreated) Larva Larva Tomato leaf extract Basil leaf extract (Photos: J.B. Sulifoa, 2005) 137

156 Appendix 7 (continued) Larva Larva Custard apple leaf extract Soursop leaf extract Larva Larvae African marigold whole plant extract Pawpaw leaf extract Larva Kava root powder extract (Photos: J.B. Sulifoa, 2005) 138

157 Appendix 8: Pheromone traps near cabbage fields (chapter 5). 8a: Delta trap with DBM pheromone lure. 8b: Cabbage plot with pheromone trap. (Photos: J.B. Sulifoa, 2004) 139