EVALUATION OF NEW AND EXISTING INSECTICIDES FOR THE CONTROL OF WALNUT HUSK FLY 2012

Transcription

1 EVALUATION OF NEW AND EXISTING INSECTICIDES FOR THE CONTROL OF WALNUT HUSK FLY 2012 William W. Coates and Robert A. Van Steenwyk ABSTRACT Dilute, full coverage treatments of pyrethroid and neonicotinoid insecticides combined with Nu- Lure Insect Bait and Dyne-Amic provided excellent (Danitol + Belay, Brigadier) or good (Triple Crown) control of walnut husk fly (WHF). Neonicotinoids plus Nu-Lure Insect Bait and Dyne- Amic also provided excellent (Assail) or good (Belay) control of WHF. A pyrethroid (Warrior II) or organophosphate (malathion) treatment combined with Nu-Lure Insect Bait and Dyne- Amic each provided good WHF control. Exirel 10SE (cyazypyr), an anthranilic diamide, did not reduce WHF damage and does not appear to be an effective WHF control material. OBJECTIVES The objective of this research project was to test new, reduced risk chemical treatments for WHF control compared to existing standard control measures utilizing full coverage, dilute sprays with added insect bait. SIGNIFICANT FINDINGS 1. Dilute, full coverage combination treatments of pyrethroid and neonicotinoid insecticides combined with Nu-Lure Insect Bait and Dyne-Amic provided good to excellent WHF control. Danitol 2.4EC (fenpropathrin) + Belay 2.13SC (clothianidin) and Brigadier (bifenthrin + imidacloprid) provided excellent control while Triple Crown (bifenthrin + zeta-cypermethrin + imidacloprid) provided good control. 2. Dilute, full coverage treatments of neonicotinoid insecticides combined with Nu-Lure Insect Bait and Dyne-Amic provided good to excellent WHF control. Assail 30SG (acetamiprid) provided excellent control. Belay 2.13SC (clothianidin) was not significantly different but had numerically higher WHF damage than Assail. Belay 2.13SC was not significantly different compared to the untreated check. 3. Dilute full coverage treatments of pyrethroids or organophosphates combined with Nu- Lure Insect Bait and Dyne-Amic provided good control. These included the grower standard organophosphate (Malathion 57%) as well as the pyrethroid Warrior II (lamdacyhalothrin). 4. Exirel 10SE (cyazypyr), a new anthranilic diamide insecticide, does not appear to be a good WHF control material. California Walnut Board 215 Walnut Research Reports 2012

2 PROCEDURES The test orchard was a block of Hartley walnuts located just south of Hollister in an area noted for high WHF populations. Foliar sprays were applied with a hand-gun orchard sprayer operating at 250 psi with a finished spray volume of approximately 300 gal/acre. Each treatment was replicated four times with individual tree replicates in a randomized, complete block design. There were buffer trees between each treated tree. All treatments including the treated check included Nu-Lure Insect Bait at 0.365% and Dyne-Amic at % V/V. Treatments were applied 24 July, 14 August and 31 August. The adult WHF population was monitored by using two yellow un-baited apple maggot panel traps super-charged with ammonium carbonate dispensers. These traps were inspected weekly with the removal of flies and replacement of the ammonium carbonate. WHF damage was evaluated on 29 August by the visual examination of 100 nuts per replicate for stings, larval damage and exit holes combined into total infestation. These nuts were not removed from the tree. On September 19, at the beginning of hull-split and shortly before commercial harvest, 250 nuts per replicate were evaluated for infestation. These were removed from the tree and dissected to determine larval instar. RESULTS The adult WHF population showed three distinct peaks in trap catches which were followed by dramatic population drops as a result of insecticide applications (Fig. 1). The first peak occurred on 24 Jul and the experimental insecticides were applied the same day. This caused the population to significantly decline for about two weeks. The population then resurged on 14 Aug and a second application of the experimental insecticides was applied on that date. Although the WHF population again declined, it resurged more rapidly and a third application of experimental insecticides was applied on 31 Aug. Based upon nut damage, it appears we were about one week late on each application and possibly four applications might have been necessary to suppress the WHF population below damaging levels. At the mid-season inspection of 100 nuts (29 Aug), WHF damage varied widely from 4.3 to 17.0 percent but there were no significant differences between treatments possibly due to small sample size (Table 1). This evaluation was about five weeks after the first spray application and two weeks after the second application. The pre-harvest evaluation of 250 nuts per replicate was made on 19 Sep about two months after the first spray application and three weeks after the last application (Table 1). There were no significant differences between treatments for stings or for a combination of first and second instar larvae. The combination of third instar larvae and exit holes showed a significant difference among the treatments. Danitol 2.4EC + Belay 2.13SC, Brigadier and both rates of Assail had significantly lower infestation compared to the treated check. Triple Crown, Warrior II, Malathion 57% (the grower standard) and Belay 2.13SC were numerically lower than the treated check but not significantly lower. Exirel 10SE had a numerically higher infestation than the treated check but not significantly higher. The total infestation showed a similar pattern of infestation and treatment differences with Danitol 2.4EC + Belay 2.13SC, Brigadier, and both California Walnut Board 216 Walnut Research Reports 2012

3 rates of Assail having significantly lower infestation compared to the treated check. Triple Crown, Warrior II and Malathion 57% were numerically lower than the treated check but not significantly lower and Exirel was numerically higher than the treated check but not significantly higher. DISCUSSION Danitol 2.4 EC + Belay 2.13SC, Brigadier and two rates of Assail provided excellent control of WHF with full coverage, dilute sprays combined with Nu-Lure Insect Bait and Dyne-Amic. Triple Crown, Malathion 57%, Warrior II and Belay 2.13SC provided numerically good control of WHF but not significantly better than the untreated control. Exirel 10SE did not reduce WHF damage. Neonicotinoid insecticides are believed to have some systemic ability against WHF larvae 1. This may explain the improved efficacy of neonictinoid-containing treatments versus the organophosphate and pyrethroid only treatments since some damage appeared to occur before our first treatment. This differential efficacy may not apply if treatments are applied as low volume bait sprays that do not achieve full coverage. Exirel 10SE is not registered on English walnuts in California as of December, REFERENCES 1. Coates, William W and Robert A. Van Steenwyk Evaluation of Selected Insecticides for Walnut Husk Fly Control Walnut Research Reports 1997: Walnut Marketing Board, Sacramento, CA. California Walnut Board 217 Walnut Research Reports 2012

4 California Walnut Board 218 Walnut Research Reports 2012 Table 1. Mean number of walnut husk fly infested nuts during a time search and in the harvest sample in Hollister, CA 2012 Mean a number of infested nuts Treatment Rate form/ac Mean a percent infested nuts Stings 1st and 2nd instar 3rd instar & exits Total infestation Danitol 2.4EC b fl. oz. 4.3 a 0.0 a 0.3 a 3.4 d 3.7 d Belay 2.13 SC 3.0 fl. oz Belay 2.13SC b 3.0 fl. oz 14.0 a 0.1 a 0.6 a 11.1 abc 11.8 abc Brigadier b 12.8 fl. oz 9.0 a 0.1 a 1.0 a 4.5 cd 5.6 cd Triple Crown b 10.3 fl. o. 9.3 a 0.0 a 0.4 a 7.7 bcd 8.1 ab Assail 30SG b 6.0 oz. 4.3 a 0.0 a 0.3 a 4.5 cd 4.8 cd Assail 30SG b 4.0 oz. 7.0 a 0.0 a 0.6 a 5.7 cd 6.3 cd Exirel 10SE b 20.5 fl. oz a 0.0 a 1.9 a 16.1 a 18.0 a Warrior II b 2.56 fl. oz. 8.3 a 0.0 a 1.2 a 9.1 abcd 10.3 bcd Malathion 57% b 48.0 fl. oz a 0.0 a 0.4 a 9.6 abcd 10.0 bcd Treated check b a 0.1 a 0.9 a 14.0 ab 15.0 ab a Means followed by the same letter in a column are not significantly different (Fisher's Protected LSD, P 0.10). b Treatments included Dyne-Amic at % V/V and Nu-Lure at 0.365%

5 California Walnut Board 219 Walnut Research Reports 2012 Fig. 1 Mean number of WHF captured per trap per day in Hollister, CA st Application 2 nd Application 24 July 14 August 3 rd Application 31 August