R. A. Van Steenwyk,L. W. Barclay, W. W. Barnett, P. S. McNally, W. H. Olson, W. R. Schreader, G. S. Sibbett and C. V. Weakley

Transcription

1 INVESTIGATIONS ON NAVEL ORANGEwORMCONTROL IN WALNUTS R. A. Van Steenwyk,L. W. Barclay, W. W. Barnett, P. S. McNally, W. H. Olson, W. R. Schreader, G. S. Sibbett and C. V. Weakley Navel orange worm populations can be monitored using a modified NOW egg trap. The trap should be painted black and baited with ground almond press cake plus 10% crude almond oil. It appears from our first year of study that a husksplit treatment scheme based on NOW egg trap counts might be possible. The results indicate that treatment at a population level of around 0.75 eggs/trap/day from July 1 to husk-split for nuts to be harvested prior to 2 weeks after husk-split would prevent economic loss. The population level for treatment then moves progressively lower as the time period between husk-split and harvest lengthens, until harvest is more than 4 weeks after husk-split. At that time interval, any NOW activity would indicate the need for treatment. In the insecticide screening studies, Guthion gave the best NOW control registered materials tested. Guthion did not cause flare-ups of spider or walnut aphids in our study, as has been reported by others. OBJECTIVES of the mites To develop a husk-split treatment scheme for navel orangeworm (NOW) control based on NOW egg traps and to develop phenological models for NOW to predict which years will be outbreak years and which orchards will be most likely to become heavily infested. PROCEDURES Population monitoring. A number of walnut orchards were monitored for codling moth and NOW in Tulare, San Joaquin and Sutter/Butte counties in Codling moth was monitored by placing 4 Pherocon IC traps in each orchard in late March or early April and inspecting the traps twice a week until harvest. The pheromone was changed once a month and the bottoms of the traps were changed when necessary. NOW was monitored by placing 8 NOW egg traps in each orchard in early April and inspecting the traps twice a week until harvest. The NOW egg traps were painted black and were baited with ground almond press cake plus 10% crude almond oil. The bait was changed once a week. Both codling moth and NOW traps were placed in a uniform manner in each orchard. After husk-split was well underway, 50 nuts from around each codling moth trap (200 nuts per orchard) were inspectedfor codling moth and NOW damage. At grower harvest, 250 nuts around each codling moth trap (1000 nuts per orchard) were inspectedfor codling moth and NOWdamage. Insecticide screening. Two studies on codling moth and NOW control were conducted in 1983, one at Westside Field Station and the other in Tulare County. At the Westside Field Station, 5 treatments were replicated 8 times in a randomized complete block design. The treatments were Guthion 50% WP at 2.0 lb ai/ac, Pounce 3.2 EC at 0.2 lb ai/ac, FMC EC at 0.08 lb ai/ac, SLJ % WP at 0.5 lb ai/ac and an untreatedcontrol. Each replicatewas an

2 individual tree (Serr variety). The treatments were applied at husk-split (Aug. 31) with a hand-held orchard sprayer operating at 200 PSI. All materials were applied at 540 gal water/ace At harvest (Oct. 5), 100 nuts per replicate (800 per treatment) were inspected for codling moth and NOW larvae and damage. To determine the effect of the materials on spider mite populations, 10 terminal leaflets per tree were brushed on 9/7, 9/14, 9/24 and 10/5 and the spider mites were counted. In the Tulare County trial, which was conducted by Steve Sibbett, Guthion 50% WP at 1.5 lb ai/ac and Lorsban 50% WP at 2.0 lb ai/ac were compared. Each treatment was replicated 4 times in alternating 10-acre plots across an 80-acre block of Payne walnuts. The treatments were applied on June 20 for codling moth control and again at husk-split (Aug. 29) for codling moth and NOW control. The June treatment was made by commercial ground rig at 300 gal water/ac and the August treatment by helicopter at 30 gal water/ace The effect of the treatments on walnut aphid populations was determined by counting the aphids on 100 leaflets per replicate weekly from June 27 through Sept. 6. On the last two sample dates (9/1 and 9/6), only 50 leaflets per replicate were sampled. When observations in the plots showed that spider mite populations were beginning to increase, 100 leafets per replicate were brushed and counted weekly from July 11 through Aug. I, except on 7/18, 7/25 and 8/8 when only 50 leaflets were sampled. At commercial harvest (Aug. 13), 250 nuts per replicate were inspected for NOW and codling moth larvae and damage and for shriveled nut meats. RESULTS Population monitoring. The navel orangeworm population, number of days from husk-split to harvest, and amount of NOW infestation varied considerably in the three study areas (Table 1). We calculated the NOW population, as eggs per trap per day (E/T/D), for three time periods: from beginning of trapping to harvest, from July 1 to husk-split, and from beginning of trapping to husksplit. The period from beginning of trapping to harvest includes the population for the entire season. Since most insecticides registered for NOW control (Guthion, Zolone, Sevin) should be applied at or before husk-split, a shorter, commercially-feasible period of egg trap monitoring, such as from July 1 to husk-split, could be used to indicate the need for treatment. Increases in egg trap counts in the period between beginning of trapping to husk-split and beginning of trapping to harvest indicate a large population of NOW after husksplit, and the potential for late season NOW damage to nuts. In the Tulare County orchards, the number of days from husk-split to harvest varied from 11 to 25 and the NOW population was in general much higher than in the San Joaquin or Sutter/Butte orchards, ranging from 0.09 to 1.52 E/T/D for the entire season (Table 1). Two orchards (T3, T6) which had large NOW egg trap counts also had large NOW nut infestations, despite the fact that T3 had received a husk-split spray. In the San Joaquin County orchards, the number of days from husk-split to harvest was prolonged, ranging from 29 to 35 days, and the NOW population was moderate, ranging from 0.31 to 0.70 E/T/D for the season. NOW nut infestation was considerable in all San Joaquin orchards except S4 which was harvested 29 days after husk-split. In Sutter/Butte County orchards, the number of days from husk-split to harvest was quite variable, ranging from 10 days (the earliest harvest of all orchards) to 40 days (the

3 latest harvest of all). The NOW population was also quite variable, ranging from 0 to 0.61 E/T/D for the season. NOW did not cause a great deal of damage except in orchard Bl. However, about half of the orchards (B2, B3, B5, and most of Bl) were sprayed at husk-split for NOW control. In the Bl orchard, a small portion (about 2 acres) was left untreated and the remainder was treated 23 days after husk-split with Supracide, which has a 7-day preharvest interval. There was a marked reduction in the amount of NOW-damaged nuts as a result of this treatment. Thus, even if a large population of NOW develops after husksplit, corrective measures can be taken. When all the orchards are ranked from the shortest to longest interval between husk-split and harvest, a general trend of increasing NOW damage is apparent (Table 2). This illustrates the importance of early harvest for NOW control. Nut damage due to NOW also tended to increase with increased NOW populations, as measured by egg trap counts. For example, T6, which was harvested 25 days after husk-split, had a very high egg count and the highest damage. It appears that the NOW egg count indicating a need to treat will be progressively lower the longer the split nuts are to remain on the trees. Based on this first year of study, orchards harvested within 2. weeks after husk-split can withstand sulstantial NOW populations without serious economic loss if treated at a population level of around 0.75 E/T/D from July I to husksplit. When the harvest is between 2 and 3 weeks after husk-split, the population level indicating treatment should be lowered to around 0.50 E/T/D. For harvest between 3 and 4 weeks after husk-split, the level should be further lowered to around 0.25 E/T/D. For harvest more than 4 weeks after husk-split, a treatment should be applied when any NOW activity is observed between July 1 and husk-split. Egg trap counts could also be used to indicate which orchards need to be harvested first or as early as possible. Since currently registed insecticides for NOW will provide 50% to 80% control at best, orchards with large NOW egg counts could be harvested earlier through the use of Ethephon, thus avoiding much of the damage that would be caused by NOW. Insecticide screening. In the WestsideField Station trial, both FMC and Guthion gave excellent control of NOW (Table 3). Pounce and SLJ 0312 gave some control but neither was significantly different from the untreated. There were very few codling moths in the plot, so codling moth control could not be evaluated. Spider mite populations did not flare-up following the application of Guthion, FMC or Pounce (Table 4), as has been reported by others. SLJ 0312 provided excellent control of spider mites. However, because the spider mite populations were extremely variable, cifferences between treatments were not significant. In the Tulare County trial, neither Lorsban nor Guthion gave satisfactory control, with of the Lorsban-treated nuts and 7.6% of the Guthion-treated nuts damaged or infested by NOW and codling moth (Table 5). Although Guthion gave slightly better control of NOW and codling moth than Lorsban, the difference was not significant. Lorsban appeared to cause a flare-up of spider mites (Table 6). Spider mite counts were much higher in the Lorsban-treated plots at all sampling dates but because of the high variability, differences were significant only on the last date. Neither material caused a flare-up of walnut aphid. There were more aphids in the Guthion-treated plots, but the difference was not significant (Table 7). 92.

4 CONCLUSIONS Population monitoring. It appears from our first year of study that a husksplit treatment scheme based on NOW populations as measured by egg traps might be possible. However, the population level indicating treatment will not be a fixed number but will vary depending on the anticipated days from husk-split to harvest since the longer the interval between husk-split and harvest, the longer the susceptible nuts are exposed to NOW. Preliminary results indicate that treatment at a population level of around 0.75 E/T/D from July I to husksplit for nuts to be harvested prior to 2 weeks after husk-split would prevent economic loss. The level then progressively lessens as the time period between husk-split and harvest lengthens, up to a harvest later than 4 weeks after husk-split. With that length of interval between husk-split and harvest, any NOW activity indicates the need for treatment. Since orchards with high egg counts are more likely to become heavily infested the longer the nuts remain on the trees after husk-split, the egg traps could also be used to indicate which orchards need to be harv~sted first or as early as feasible. Insecticide screening. Guthion, which was the only registered material for use on walnuts that we tested, ~ave 600d control of NOh in the Westside Field Station trial. It is hard to judge the effectiveness of either Guthion or Lorsban in the Tulare County trial because there was not an untreated control. In our trials Guthion did not cause a flare-up of either walnut aphid or spider mites. Guthion has been reported by others to do so, however. Thus, we recommend the application of Guthion if a large population of NOW, as measured by NOW egg trapping, exists in the orchard at husk-split. However, if spider mites have been a problem in the past, a miticide should be included. Next year we will compare Guthion to other registered materials such as Zolone, Supracide and Sevin. 93.

5 Table 1. Orchard Characteristics, Navel Orangeworm Egg Trap Counts, and Navel Orangeworm and Codling Moth Damage in Tulare, San Joaquin, and Sutter/Butte Counties, 1983 Days from Avg. no. NOW eggs/trap/day: AVf!.% Av'2..% Field split husk-split Beginning date to: July 1 No. Varietv soray to harvest Husk-solit Harvest to solit dama2e damal!e Tulare - T 1 Various No 19 0.H T 2 Ashley No T 3 Payne Yes T 4 Payne No T 5 Payne No T 6 Payne No Hartley San Joa.9.uin S 1 Payne No S 2 Payne No S 3 Payne No S 4 Payne No Sutter/ Butte B 1 Ashley Yes No B 2 Ashley Yes Lompoc B 3 Ashley Yes B 4 Tehama No 22/ /0 2.6/1.1 B 5 Ashley Yes B 6 Vina o 13 O.3H B 7 Hartley Ashley No

6 Table 2. Orchard Characteristics, Navel Orangeworm Egg Trap Counts, and Navel Orangeworm and Codling Moth Damage, Ranked from the Shortest Interval between Husk-Split and Harvest to the Longest Interval, 1983 Days from Avg. no. NOW eggs/trap/day: Avg. % Av'il... % Field husk-split Beginning date to: July 1 NOW No.* Variet to harvest Husk-s lit Harvest to s lit dama e damaee B 3 Ashley Yes T 2 Ashley No T 5 Payne No B 6 Vina No Hartley T 4 Payne No B 5 Ashley Yes T 3 Payne Yes B 7 Ashley No T 1 Various No B 4 Tehama No 22/ /0 2.6/1.1 T 6 Payne No Hartley B 2 Ashley Yes Lompoc S 4 Ashley No S 1 Payne No S 2 Payne No S 3 Payne No B 1 Ashley Yes No *B = Sutter/Butte, T = Tulare, S = San Joaquin 95.

7 Table 3. Control of Navel Orangeworm and Codling Moth with Various Insecticides at WSFS, 1983 Mean* percent nuts infested or damaged by: Navel orangeworm Codling moth Larvae Treatment present Damage Total Damage Total FMC a 0 a 0.4 a 0 a 0.4 a Guthion 0.6 a 0 a 0.6 ab 0 a 0.6 a Pounce 0.9 a 0.3 ab 1.1 bc 0.1 a 1.2 ab SLJ ab 0.5 b 1.9 bc 0.1 a 2.0 bc Control 2.5 b 0.1 ab 2.6 c 0 a 2.6 c *Means followed by the same letter in a vertical column are not significantly different at the 5% level ( DMRT>. Table 4. Effect of Various Insecticides on Spider Mite Populations at WSFS, 1983 Treatment Mean. number and standard deviation of spider mites/lo leaflets on: 9/7 9/14 9/23 10/5 SLJ i : t t 9.2 Pounce 2.2 t t t t FMC ~ t t t Guthion 13.0 t t t 64.5 Control 17.0 :t :t :t :t *Due to the extremely large variability, there were no significant differencesamong treatmentsat the 54 level (DMRT)

8 Table 5. Control of Navel Orangeworm and Codling Moth with Guthion and Lorsban in Tulare Co., 1983 Mean* percent nuts infested Total by larvae of: percent Treatment Navel orangeworm Codling moth damage Guthion 3.2 a 0.5 a 7.6 a Lorsban 4.5 a a *Means followed by the same letter in a vertical column are not significantly different at the 57- level (Student's T). Table 6. Effect of Guthion and Lorsban on Spider Mite Populations in Tulare Co., 1983 Mean* no. of spider mites/leaflet on: Treatment 7/11 7/18 7/25 8/1 Guthion 0.04 a 0.14 a 0.20 a 0.05 b Lorsban 0.21 a 1.18 a 2.69 a 1.73 a *Means followed by the same letter in a vertical column are not significantly different at the 5% level (Student's T). 97.

9 Table 7. Effect of Guthion and Lorsban on Walnut Aphid Populations in Tulare Co., 1983 Mean* no. walnut aphids/leaflet on: Treatment 6/27 7/5 7/11 7/18 7/25 8/1 8/8 8/15 8/22 9/1 9/16 Lorsban 0.02 a 0.2 a 1.2 a 3.3 a 5.2 a 4.5 a 1.4 a 1.3 a 1.3 a 0.2 a 0.6 a \.0 00 Guthion 0.06 b 0.4 a 1.9 a 2.9 a 6.2 a 7.9 b 2.9 b 2.7 a 3.0 B 1.7 a 4.2 a *Means followed by the same letter in a vertical column are not significantly different at the 5% level (Student' s T).