Timing of bollworm, Helicoverpa zea, infestation across cotton planting dates and impacts on yield in the southeastern US

Bollworm, Helicoverpa zea, is a major pest of cotton across the southern US. Impacts of cotton planting dates on bollworm infestation timing and severity are understudied. We planted cotton in various locations across the southeastern US to represent early, timely, and late planting dates for each respective region during 2020 and 2021. In 2021, we also protected plots from bollworm using insecticide, while leaving other plots untreated. We sampled bollworm larvae and assessed cotton damage during the season. We assessed impacts on yield using plant mapping, box mapping, and machine harvest. In general, bolls retained on the plant, and grams of seed cotton was highest in early-planted and sprayed cotton compared to later planted and unsprayed cotton. In contrast bolls damaged by caterpillars was lower in early-planted sprayed cotton compared to later planted and unsprayed cotton. In North Carolina during 2021- a high-pressure location- even though the number of first position bolls was not different between sprayed and unsprayed plots, the seed cotton produced by these bolls contributed greatly to yield, with more seed cotton in first position bolls regardless of spray; more seed cotton was from first position bolls in sprayed plots than first position bolls in unsprayed plots. Forth position bolls contributed to yield in unsprayed plots, but not in sprayed plots, indicating plant compensation. Finally, yield shifted to the lower nodes as planting date became later, except under high bollworm pressure. This study highlights the compensatory ability of cotton to bollworm feeding, especially in early-planted cotton.