AP249 Biological control of apple powdery mildew. Shane Dullahide Queensland Department of Primary Industries

AP249 Biological control of apple powdery mildew Shane Dullahide Queensland Department of Primary Industries

AP249 This report is published by the Horticultural Research and Development Corporation to pass on information concerning horticultural research and development undertaken for the apple & pear industry. The research contained in this report was funded by the Horticultural Research and Development Corporation with the financial support of the Incitec Limited. All expressions of opinion are not to be regarded as expressing the opinion of the Horticultural Research and Development Corporation or any authority of the Australian Government. The Corporation and the Australian Government accept no responsibility for any of the opinions or the accuracy of the information contained in this Report and readers should rely upon their own inquiries in making decisions concerning their own interests. Cover Price $20.00 HRDC ISBN 1 86423 433 4 Published and Distributed by: Horticultural Research and Development Corporation Level 6 7 Merriwa Street Gordon NSW 2072 Telephone: (02)9418 2200 Fax: (02)9418 1352 Copyright 1996

INDUSTRY SUMMARY 1 TECHNICAL SUMMARY 2 FINAL REPORT - Introduction 3 - Summary 3 - Description of Proj ect 4 - Assessments 5 - Results 7 - Discussion 8 APPENDIX 1 - Spray application dates - Rainfall October 1993 to February 1994 - Temperature on spray application days - Relative humidity after spraying - Field trial plan APPENDIX 2-1992-93 field trial

Jonathan apple tree fruiting spur leaves infected with powdery mildew Jonathan apple fruiting spur leaves with powdery mildew parasitised with AQIO

INDUSTRY SUMMARY Apple powdery mildew fungal disease is a minor problem on the majority of commercial apple varieties, but many new varieties such as Royal Gala, Fuji and Braebum are more susceptible and will require more vigilant control measures. This project reports the field testing of a biological product - AQIO, when used to replace or reduce the number of fungicide sprays required for powdery mildew control. In field trials on the apple cultivars Jonathan and Granny Smith of high and moderate susceptibility to powdery mildew, AQIO was applied alone or as a substitute for Nimrod or Saprol in spray schedules. Apple powdery mildew fungicide applications were reduced by at least 50 percent and acceptable levels of powdery mildew maintained, where the biological product AQIO was substituted for fungicide applications. The predator mite populations were not affected by regular the applications of AQIO. AQIO is a biological product which is dependent on moist weather conditions following application for successful powdery mildew control. The formulation used in these trials gave unsatisfactory powdery mildew control, when applied under dry weather conditions suitable for normal pesticide spraying. The compatibility of AQIO as a tank mix with fungicides, insecticides and plant nutrients was not tested in this work. The trial trees received regular azinphos-methyl applications with no apparent effect on AQIO and subsequent powdery.mildew control.

TECHNICAL SUMMARY The field trials in this project show the potential of the biological product AQIO to reduce fungicide use for the fungal disease powdery mildew in apples by at least 50 percent. When applied under suitable weather conditions, AQIO alone or in combined spray schedules with either bupirimate (Nimrod ) or triforine (Saprol ) maintained powdery mildew on Jonathan or Granny Smith trees at acceptable levels. AQIO as a biological produce requires moist conditions following application for successful establishment and powdery mildew control. Weather records from these trials indicate that fewer AQIO applications, applied during the most suitable weather periods, could give similar results. The present formulation of this product is unsuitable for application during normal spraying conditions of fine dry weather. The commercial cooperator Incitec (Crop Care) has disbanded the biological development and formulations section since the commencement of this work. Development of specific formulations for biological products which enhances their viability in normal pesticide application weather conditons is needed for commercial adoption of these products to reduce present pesticide usage.

INTRODUCTION Apple powdery mildew is a debilitating disease causing reduced tree vigour and productivity through infection of vegetative shoots, flower buds and infected fruit. The disease is caused by the fungus Podosphaera leucoiricha. The powdery mildew fungus grows as a parasite on the surface of leaves, shoots, twigs, blossoms and fruit, extracting nutrients from underlying tissues. White to light-grey powdery patches develop rapidly to cover both leaf surfaces, causing curling, stunting and death. A similar white, powdery growth to that on the leaves causes stunting and dieback of shoot growth. Tips of fruiting twigs and terminal growth of shoots are extremely vulnerable. The fruit and leaf buds become coated with mildew and fail to develop fully. Affected blossoms frequently wither and fruit fails to set. Powdery mildew manifests itself on fruit as a skin russet composed of a maze of fine lines, often appearing as a solid patch. Fruit size may be reduced, with fruit yields diminishing each season in orchards where powdery mildew disease levels are not maintained at low levels. This disease is presently managed by regular fungicide applications throughout the tree growth period. Decisions by the Australian Apple and Pear Growers Association to reduce pesticide usage by 75% by the year 2000 has meant that alternative methods for apple powdery mildew management are needed. The aims of this project were to field test a fungal hyperparasite AQIO (MIO) alone or in combined spray schedules with recommended fungicides for field control of powdery mildew to replace or substantially reduce the number of fungicide sprays required for disease control. The financial support to conduct this research, from Crop Care Australasia and the Australian Horticultural Development Corporation, is gratefully acknowledged. SUMMARY 1992-93 field trial (Appendix 1) AQIO alone, when applied under ideal wet and humid weather conditions, or as an alternative to either Nimrod (buprimate) or Saprol (triforine) in a schedule to reduce the fungicide applications by 50 percent, maintained powdery mildew leaf and bud infections on Jonathan trees at low levels. Fruit surface russet and tree yields were similar for all treatments. A full 1992-93 field trial report is attached (Appendix 1).

DESCRIPTION OF THE PROJECT (i) General Objectives To develop a field use strategy for biological agent (AQIO) for apple powdery mildew control. To reduce apple powdery mildew pesticide usage by at least 50%. Maintain powdery mildew disease levels equal to a conventional fungicide schedule. 1993-94 field trial objectives To field test AQIO in an integrated apple disease spray schedule and evaluate for: (a) powdery mildew disease levels. (b) two-spotted and predatory mite populations. To record environmental data at trial site. (ii) Procedure Conduct a field trial on mature Jonathan and Granny Smith apple trees at the Granite Belt Horticultural Research Station, Applethorpe. Treatments: Spray treatments are listed in Table 1. Application: All treatments were applied with a hand held spray wand at high volume spray rates of approximately 1500 litres per hectare on the dates shown in Table 2. Treatment plots: Single, wide spaced (6 m x 6 m), mature trees with a history of high powdery mildew levels. Trial design: Randomised block with six replicates of three Jonathan and three Granny Smith trees. Plan of field trial is shown in Figure 4. Environmental data Rainfall: Dates of rainfall and amount recorded are shown in Figure 1. Temperature: Maximum and minimum temperatures on days when sprays were applied are shown in Figure 2. Relative humidity: The hours of relative humidity <100 percent and >100 percent, for 48 hours following AQIO spray applications are shown in Figure 3.

Table 1. Powdery mildew field trial spray treatments. Treatments Application timing Rating/100 litres 1. Saprol (triforine 190 g/l) *Apple Black Spot Warnings then, 120 ml AQIO + Tween 80 at 10-18 day intervals from 10 January 100 g 50 ml 2. Saprol *Apple Black Spot Warnings then, 120 ml AQIO +Tween 80 at 10-21 day intervals, during ideal weather from 100 g January 50 ml 3. Nimrod (bupirimate 250 g/l) From 14 October 40/60 ml 4. AQ10 + From 14 October 100 g Tween 80 50 ml Or Nimrod (bupirimate 250 g/l) 40/60 ml 5. AQIO + Tween 80 10-21 days, from 14 October during ideal wet weather 100 g 50 ml 6. Unsprayed * Apple black spot (Venturia inaequalis) warnings from 14 October to 23 December. ASSESSMENTS Powdery mildew disease incidence Jonathan - leaves The third and fourth fully developed leaves from tips of 25 randomly selected summer shoots were collected in December 1993, March and May 1994. These were examined in the laboratory for presence of active powdery mildew (Table 3) and for the percentage leaf area covered by powdery mildew fungal growth (Table 4). Jonathan - shoots Fifty summer shoot tips per tree were selected at random in May 1994, and rated for the presence of active powdery mildew infection of the terminal bud (Table 5). Granny Smith - leaves In March 1994, 50 leaves were selected and rated for powdery mildew by the methods used for the Jonathan leaves (Table 6). Mites In April 1994, 20 mature leaves per tree were randomly selected from the inside lower tree canopy and the number of adult predatory mites Typhlodromus pyri as well as the two-spotted leaf feeding mites Tetranychus urticae recorded (Table 7).

Table 3. Jonathan trees - powdery mildew infected leaves. Treatment 1. Saprol then AQ10 (8-18 days) 2. Saprol then AQIO (10-21 days) 3. Nimrod 4. AQIO or Nimrod 5. AQIO (8-18 days) 6. Unsprayed Percent infected leaves 20-12-93 7-3-94 13-5-94 21 26 13.5 28 30.1 13 15 9 8.5 30.5 25.5 23 48.5 31.5 21 84 64 47 17.6 11.8 17 LSD (P = 0.05) 17.6 11.8 17 Table 4. Jonathan trees - powdery mildew infected leaves. Treatment 1. Saprol then AQIO (8-18 days) 2. Saprol then AQIO (10-21 days) 3. Nimrod 4. AQIO or Nimrod 5. AQIO (8-18 days) 6. Unsprayed LSD (P = 0.05) Percent leaf area infected 20-12-93 7-3-94 13-5-94 19.3 17.8 16.7 23.6 19.1 16.2 17.4 10.3 24.8 19.9 19.3 17.9 17.7 15.9 18.8 31.4 23.2 27.8 9.4 5.8 12.3 Table 5. Jonathan trees - summer shoots. Treatment 1. Saprol then AQ 10 (8-18 days) 2. Saprol then AQIO (10-21 days) 3. Nimrod 4. AQIO or Nimrod 5. AQIO (8-18 days) 6. Unsprayed LSD (P = 0.05) Percent summer shoot terminal bud infection 12.5 11.1 4.0 9.3 15.3 23.8 7.9 Table 6. Granny Smith trees - powdery mildew infected leaves. Treatment Percent infected leaves Percent leaf area infected 1. Saprol then AQ 10 (8-18 days) 2. Saprol then AQIO (10-21 days) 3. Nimrod 4. AQIO or Nimrod 5. AQIO (8-18 days) 6. Unsprayed LSD (P = 0.05) 7.5 8 8.5 15.5 13 27.5 7.7 5.8 11.5 6.3 8.9 10.8 12.2 NS

Table?. Number of Tj/jft/orfromMS/rvri (predatory mites) and two-spotted mites ( (Tetranychus urticae) on 20 leaves per tree. Treatment 1. Saprol then AQ10 (8-18 days) 2. Saprol then AQIO (10-21 days) 3. Nimrod 4. AQIO or Nimrod 5. AQIO (8-18 days) 6. Unsprayed LSD (P = 0.05) Mites T. pyri Two-spotted 32.5 21.5 55.5 43.3 49.3 27.5 NS.8.5.5 1.5.5.3 NS RESULTS Powdery mildew All treatments reduced powdery mildew disease levels in the Jonathan and Granny Smith trees. Jonathan trees (highly susceptible to powdery mildew). All spray treatments reduced the number of powdery mildew infected leaves, as well as leaf area and summer shoot terminal buds with active powdery mildew fungal growth, in comparison with unsprayed trees. When AQIO spray intervals were extended to 10 to 21 days throughout the season the percent infected leaves and terminal shoot infection with powdery mildew were greater than trees sprayed with Nimrod. Granny Smith trees (moderately susceptible to powdery mildew). All treatments reduced the percent leaves with powdery mildew in comparison with unsprayed trees, but there was no significant reduction in leaf area with active powdery mildew growth. Mites The predatory mite populations present in the trees, were not affected by the treatments applied throughout the season.

DISCUSSION Fungicide reduction by 50 percent or greater was possible by the substitution of AQIO applications for fungicide applications without loss of powdery mildew control over two seasons. AQIO has the potential to maintain acceptable low levels of apple powdery mildew, when used alone, and either following triforine applied in spring and early summer, or alternating with bupirimate throughout the season. As a biological formulation, the establishment and effect of AQIO on powdery mildew is dependent on moist or wet weather conditions following application. AQIO spray schedules may be extended beyond 10 days while maintaining powdery mildew control, when applications coincide with wet weather periods. The rainfall, temperature and relative humidity recordings in Figures 1, 2 and 3 show that following the applications of AQIO possibly only three dates - 6 December, 11 February and 17 February were ideal for AQIO establishment in the tree canopy. Few applications of AQIO may be necessary each season, if these are applied under moist weather that is sustained for a period following application. A formulation that could provide this environmental protection for this product would allow application at any time suitable to orchard operations.

Table 2. Apple powdery mildew field trial - spray application dates 1993-94. Treat no. Date of application October November December January 14 20 25 29 9 22 6 23 10 14 19 1 S S S S AQIO AQIO 2 s S s S AQIO AQIO 3 N.4 N.4 N.4 N.6 N.4 N.6 N.4 4 AQIO AQIO N.4 N.6 AQIO AQIO N.4 5 AQIO AQIO AQIO AQIO AQIO AQIO AQIO AQIO 6 UNSPRAYED AQIO = fungal hyperasite formulation, 1 g/l N = Nimrod.4 or.6 ml/l S = Saprol 1.2 ml/l

Figure 1 40 RAINFALL OCTOBER-FEBRUARY 1993-1994 30 E E 20 c a: 10 0 H Mi M HlH m trm III I. I III 5 15 17 19 22 25 31 2 14 26 6 8 16 9 15 21 29 2 12 14 18 20 6 16 18 21 23 26 1 12 21 3 7 9 23 13 20 28 1 5 13 15 19 Oct Nov Dec Mont Jan Feb

igure 2 MINIMUM AND MAXIMUM TEMPERATURES ON SPRAY DAYS 1993-1994 14 20 25 29 Oct 9 22 Nov 6 ' 23 10 14 19 31 11 17 22 25 Dec Jan Feb Month

Figure 3 24 16 8 RELATIVE HUMIDITY AFTER SPRAYING 1993-1994 <100%^>100% 24 X 8 Q 24 16-8 0 5 PM 4.30 ^Q PM AM 9.30 AM 4 PM 2 PM 4 PM 3 PM 3 PM 5 PM Nov 9 Nov 22 Dec 6 Dec 23 Jan 10 Jan 19 Jan 31 Feb 11 Feb 17 Feb 25 Spray Date

Figure 4 AQ10 FIELD PLAN 1993-94 3 7 1 9 D 8 6 MP D 5 2 4 8 D 6 4 3 D B 7 1 5 B 9 D 2 1 5 3 7 7 2 D 4 6 8 D 9 I Granny Smith 9 Treatments x 6 Reps (3 Jonathan, 3 Granny Smith) Jonathan Single tree plots "D" represents dead tree "MP" represents missing tree

DPI Agricultural Production Group Horticulture - South Region PROJECT REPORT Biological Control of Apple Powdery Mildew 1992-93 Conducted by: Shane R DuUahide SENIOR EXPERIMENTALIST DIV I GRANITE BELT HORTICULTURAL RESEARCH STATION, APPLETHORPE

DESCRIPTION OF THE PROJECT (i) General Objectives. To develop a field use strategy for biological agent (MIO) for apple powdery mildew control.. To replace or reduce apple powdery mildew pesticide usage by at least 50%. Field test MIO in field tests and evaluate. To test MIO, alone or in combination with or alternating with powdery mildew fungicides, at various application timings in field trials and evaluate for: (a) powdery mildew control (b) mite population fluctuations (c) tree yields (d) fruit finish (ii) Procedure Conduct a field trial on Jonathan and Granny Smith trees at the Granite Belt Horticultural Research Station, Applethorpe. Treatments: 1. MIO (1 g/l) 2. MIO + Nimrod (.2 ml/l) 3. Nimrod (.4 ml/l) 4. MIO + Nimrod (.4 ml/l) 5. Saprol (1.2 ml/l) 6. MIO or Nimrod (.6 ml/l) 7. MIO or Saprol (1.2 ml/l) 8. MIO 9. Unsprayed Tween 80 (0.1 ml/l) added to MIO spray solutions. Treatment 1 to 7 applications at 10 to 21 day intervals. Treatment 8 applications during ideal weather conditions for MIO. Application: all treatments applied at high voltune spray rates (2000 L/ha). Application dates (Table 1). Treatment plots: single 20 year old trees. Trial design: randomised block with six replications (three Jonathan and three Granny Smith trees). Weather: Days when rainfall was received and the amotmt recorded are shown in Table 2. Maximum and minimimi temperatures on days when sprays were applied are shown in Table 3.

Table 1. Apple powdery mildew field trial - application dates 1992/93 MIO FIELD TRIAL Date of Application Treatment Number October November December 1 3 9 16 29 5 16 26 4 12 14 2 1 MIO MIO MIO MIO MIO MIO MIO M 2 MIO MIO MIO N.2 N.2 N 3 N.4 N.4 N.4 N.4 N.4 N 4 MIO MIO MIO N.4 N.4 N 5 S S S S S S 6 MIO MIO MIO N.6 N.6 N 7 MIO MIO MIO S S S 8 MIO MIO MIO MIO MIO MIO MIO 9 Un sprayed

BLE 2 RAIN DAYS 30 25 c 20-1 < 15 10 0 I imm. JU i (ijulijlijmt- 5 10 18 19 29 3(1 3-1 5 6 10 12 13 16 17 18 19 20 21 22 26 30 5 6 7 9 10 14 15 18 19 24 25 26 27 5 6 7 8 19 13 24 26 29 I 6 7 n Oct Nov Dec Jan Feb MONTH

\BLE 3 35 r TEMPERATURE 1. 3 OCT 16 29 5 16 26 4 12 14 21 31 6 12 NOV DEC JAN 22 12 FEB MIN HMAX

ASSESSMENTS Disease incidence - leaves On the Jonathan trees the third and fourth fully developed leaves from tips of 50 randomly selected summer shoots were collected from each tree in December and examined in the laboratory for presence of active powdery mildew and for percentage of leaf area covered by powdery mildew fungal growth (Table 4). Table 4. Jonathan Trees - Powdery mildew leaf infection Treatment Percent infected leaves Percent leaf area infection 1. Ml0 (8 to 10 day applications) 2. MIO or Nimrod (.2 ml/l) 3. Nimrod (.4 ml/l) 4. MIO or Nimrod (.4 ml/l) 5. Saprol (1.2 ml/l) 6. MIO or Nimrod (.6 ml/l) 7. MIO or Saprol (1.2 ml/l) 8. MIO (ideal weather applications) 9. Unsprayed 58 57 44 20 28 23 26 35 70 9 8 3 7 1 5 4 6 21 LSD (P = 0.05) 31 In February 50 Jonathan summer shoot tips were rated for presence of powdery mildew infection on the terminal bud (Table 5). Table 5. Jonathan Trees - Powdery mildew shoot infection Treatment Percent shoot terminal bud infection 1. MIO (8 to 10 day applications) 39 2. MIO or Nimrod (.2 ml/l) 36 3. Nimrod (.4 ml/l) 13 4. MIO or Nimrod (.4 ml/l) 29 5. Saprol (1.2 ml/l) 8 6. MIO or Nimrod (.6 ml/l) 17 7. MIO or Saprol (1.2 ml/l) 19 8. MIO (ideal weather applications) 23 9. Unsprayed 57 l^d (P = 0.05) 22

On the Granny Smith trees powdery mildew leaf infection was assessed similarly to the Jonathan trees in March 1993 (Table 6). Table 6. Granny Smith Trees - Powdery mildew leaf infection Treatment Percent infected leaves Percent leaf area infection 1. M10 (8 to 10 day applications) 2. MIO or Nimrod (.2 ml/l) 3. Nimrod (.4 ml/l) 4. MIO or Nimrod (.4 ml/l) 5. Saprol (1.2 ml/l) 6. MIO or Nimrod (.6 ml/l) 7. MIO or Saprol (1.2 ml/l) 8. MIO (ideal weather applications) 9. Unsprayed 37 27 15 17 11 19 18 18 25 12 8 8 9 13 13 11 8 8 LSD (P = 0.05) N.S. N.S. Disease incidence - fruit On the Jonathan and Granny Smith tree 100 fruit were selected at random per tree at harvest and rated for percent fruit surface with russet (Table 7). Table 7. Percent fruit surface with russet Treatment Jonathan Granny Smith 1. MIO (8 to 10 day applications) 2. MIO or Nimrod (.2 ml/l) 3. Nimrod (.4 ml/l) 4. MIO or Nimrod (.4 ml/l) 5. Saprol (1.2 ml/l) 6. MIO or Nimrod (.6 ml/l) 7. MIO or Saprol (1.2 ml/l) 8. MIO (ideal weather applications) 9. Unsprayed 26 21 27 16 17 20 24 17 22 4 5 4 4 4 4 5 5 6 LSD (P = 0.05) N.S. N.S.

Yield On the Jonathan and Granny Smith trees, 200 randomly selected fruit were weighed at harvest in February and March respectively (Table 8). Table 8. Weight of 200 fruit per tree (kg) Treatment Jonathan Granny Smith 1. MIO (8 to 10 day applications) 16 25 2. MIO or Nimrod (.2 ml/l) 17 24 3. Nimrod (.4 ml/l) 17 22 4. MIO or Nimrod (.4 ml/l) 17 26 5. Saprol (1.2 ml/l) 18 24 6. MIO or Nimrod (.6 ml/l) 18 22 7. MIO or Saprol (1.2 ml/l) 18 25 8. MIO (ideal weather applications) 18 23 9. Unsprayed 17 25 LSD (P = 0.05) RS^ N.S. Mites In February 50 leaves per tree were collected at random and rated for presence of active two-spotted mites (Terranychus urticae) as adults or nymphs and the number of leaves with these mites present were recorded (Table 9). Also the number of adult predatory mites {Typhlodromus pyri) present on these leaves were counted (Table 10). Table 9. Percent leaves with two-spotted mites present Treatment Jonathan Granny Smith 1. MIO (8 to 10 day applications) 2 2 2. MIO or Nimrod (.2 ml/l) 1 0 3. Nimrod (.4 ml/l) 5 2 4. MIO or Nimrod (.4 ml/l) 10 1 5. Saprol (1.2 ml/l) 1 1 6. MIO or Nimrod (.6 ml/l) 9 1 7. MIO or Saprol (1.2 ml/l) 4 3 8. MIO (ideal weather applications) 1 5 9. Unsprayed 4 5 LSD (P = 0.05) N.S. N.S.

Table 10. Number of predatory mites on 50 leaves per tree Treatment Jonathan Granny Smith 1. MIO (8 to 10 day applications) 65 75 2. MIO or Nimrod (.2 ml/l) 115 83 3. Nimrod (.4 ml/l) 125 120 4. MIO or Nimrod (.4 ml/l) 109 93 5. Saprol (1.2 ml/l) 129 88 6. MIO or Nimrod (.6 ml/l) 119 89 7. MIO or Saprol (1.2 ml/l) 194 79 8. MIO (ideal weather applications) 62 48 9. Unsprayed 140 111 LSD (P = 0.05) 65 N.S.

RESULTS MIO alone, when applied under ideal weather conditions or in spray schedules as an alternative to either Nimrod at.4 or.6 ml/l or Saprol, reduced powdery mildew leaf and bud infections on Jonathan trees. Where MIO was applied alone on an eight to ten day spray schedule, powdery mildew disease reduction was not significant. This confirms field trial results of the 1991/92 season. Powdery mildew disease reductions on Granny Smith leaves and buds from all treatments were not significantly different to unsprayed trees. Fruit weight on either Jonathan or Granny Smith cultivars were not affected by the treatments tested and fruit surface russet recorded was similar for all treatments on each cultivar. The percentage leaves with two-spotted mites present were not significantly different in the treatments tested, but the number of predatory mites on the Jonathan trees were reduced, where MIO alone was regularly applied. CONCLUSION The number of powdery mildew spray applications of either Saprol or Nimrod (at recommended rates) can be halved and powdery mildew disease levels maintained at low levels, when MIO is applied as a substitute spray in a powdery mildew scheduled spray program. Further field testing is needed to confirm these results and determine whether the continued use of MIO for more than one season on trees will improve powdery mildew control. Development of spray schedule integration of MIO is needed, where other disease and insect management parameters are considered.