Profitability of cotton, Gossypium hirsutum (L.), when controlling bollworm, Helicoverpa zea (Boddie), with variable treatment thresholds

Crops expressing Bacillus thuringiensis proteins have offered valuable crop protection benefits including reduced foliar insecticide use and crop yield protection. Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) has developed resistance to one or more Bt proteins, which consequently threatens these benefits. This has resulted in a renewed emphasis on the implementation of action thresholds for H. zea management decisions in cotton. Field experiments were conducted in College Station, TX; Stoneville, MS; and Blackville, SC, during 2020-2021 to evaluate current H. zea threshold recommendations for Texas, Mississippi, and South Carolina. Three Bt cotton technologies and five thresholds were evaluated. The Bt cotton technologies evaluated included non-Bt (NBT), Bollgard & REG; 2 (BG2; Cry1Ac + Cry2Ab), and Bollgard & REG; 3 (BG3; Cry1Ac + Cry2Ab + Vip3Aa). Across years and locations, within NBT cotton, all thresholds, including 20% oviposition, 6% fruiting forms injury, & GE;3% large larvae, and preventive sprays, resulted in greater control of H. zea and higher yield and profitability relative to non-treated NBT cotton. The threshold using 6% injury to squares and bolls was the most effective in terms of yield relative to the preventive spray. Across years and locations, the BG2 cotton 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 cotton. For BG3 cotton, spraying based on any of the thresholds was not beneficial. For NBT and BG2 cotton, thresholds of 20% oviposition, 6% injury to fruiting forms, or & GE;3% large larvae provided a reduction in insecticide applications relative to the preventive spray treatment, suggesting that these thresholds were effective triggers for controlling H. zea.