| dc.description.abstract | Experiments were conducted to devise economic thresholds for foliar insecticide applications targeting bollworms in cotton. Bt cotton technologies including TwinLink™ (TL), TwinLink Plus™ (TLP), Bollgard II® (BG2), Bollgard 3® (BG3), WideStrike® (WS), WideStrike 3® (WS3), and a non-Bt (NBT) were evaluated. A 6% fruiting forms injury threshold was selected and compared to preventive treatments utilizing chlorantraniliprole. The 6% fruiting forms injury threshold resulted in a 25 and 75% reduction in insecticide applications relative to preventive sprays for WS and BG2, respectively. Current H. zea threshold recommendations for Texas, Mississippi, and South Carolina were assessed. Three Bt cotton technologies (non-Bt, Bollgard II®, Bollgard® 3) and five thresholds (20% oviposition, 6% fruiting forms injury, >3% large larvae, preventive sprays, non-treated) were utilized. Within NBT, all treatment thresholds provided greater control of H. zea, higher yield, and profitability relative to non-treated NBT. BG2 sprayed based on 20% oviposition or preventively resulted in greater control of H. zea, and all treatments resulted in a yield or profitability equivalent to that of the non-treated BG2. Spraying BG3 based on any of the thresholds was not beneficial. In 2020-2021, sorghum was evaluated as a trap crop of H. zea and a nursery crop for natural enemies of H. zea and HearNPV dissemination into cotton. Treatments including cotton-only, non-treated cotton-sorghum, and HearNPV-treated cotton-sorghum were used. Intercropping cotton with grain sorghum did not result in a consistent increase in H. zea control and beneficial arthropods relative to the cotton-only treatment. HearNPV was detected in samples collected from all treatments indicating that the virus is naturally occurring in the locations where the study was conducted. Hence, there was no clear evidence that grain sorghum could serve as a source of HearNPV for nearby cotton. Laboratory strains of H. zea including Benzon susceptible, CRY-RR, CRY-RS, VIP-RR-70, VIP-RR-15, and TRE-RR, and 8 field-collected populations were evaluated (2021-2022) for their susceptibility to HearNPV utilizing diet-overlay bioassays. The Benzon strain was consistently more susceptible to HearNPV than any of the field populations evaluated, and the Cry-RR in 2021. However, the TRE-RR, VIP-RR-70, and VIP-RR-15 strains were as susceptible as the Benzon strain. | |
