Influence of Heliothinae (Lepidoptera: Noctuidae) pests on cotton yield components across a range of planting dates in the southeastern USA

Abstract

Because of H. zea resistance to Bt toxins, there is renewed interest in cotton IPM, including adjusting planting date. Later planted crops often receive more damage or support larger populations of Heliothinae pests, but this has not been well-documented in cotton. We explored the effects of planting date relative to Heliothinae pests in cotton across various planting windows in the southeastern USA during 2020 and 2021. In-season injury, plant mapping, box mapping, and yield were assessed. In 2021, these planting dates were split with a protective insecticide. Peak boll injury by Heliothinae larvae was not different by planting date and insecticide sprays were usually effective to minimize injury. In general, there were more bolls in position one. Boll retention was usually similar across positions, but was sometimes higher in the lower positions. Bolls that contributed the most to yield tended to be in position one or monopodia bolls, and the yield contribution tended to decrease as boll position increased. As planting date progressed, the highest percent contribution to yield tended to be on lower nodes in the plant. Yields tended to be higher in the early and middle planting dates and were higher in insecticide sprayed plots when the economic threshold was exceeded. We found clear evidence for plant compensation from H. zea feeding in one trial. Planting date relative to Heliothinae pressure level was negligible, given the plant's ability to compensate and the extended window reproductive tissue was available in earlier planting dates relative to later planting dates.