D3404: Plant architecture and canopy microclimate impacts on lepidopteran egg hatch and predation of Helicoverpa zea (Boddie) sentinel eggs

With resistance to Bt cotton developing in lepidopterous pests it's important to find alternative methods of control. In semi-arid cotton growing areas, low relative humidity and high temperatures can have an impact on hatch rates, helping to control insect pests. Late season the microclimate of the cotton canopy is more conducive to higher hatch rates and potential yield losses with a closed canopy reducing temperatures and increasing relative humidity relative to ambient conditions. Use of okra-leaf cotton may help reduce hatch rates late season by allowing greater air and light penetration into the canopy, producing a microclimate less conducive to high egg hatch. Okra cotton leaves have 55% less area than standard cotton leaves, allowing more light penetration into the canopy leading to higher temperatures and potentially less cooling respiration. (Andres et al. 2016, Mahan et al. 2016 and Pierce et al. 2022, Tellez et al. 2023, Tellez et al 2021).

Field trials with sentinel Helicoverpa zea (Boddie) eggs did show some variation in differences in hatch rates between okra leaf and standard cotton canopies. There was significantly lower egg hatch in okra-leaf cotton on two dates in July and August in 2020, with 19-27% hatch in okra-leaf vs. 51-52% in standard leaf cotton in season. One date,7/29/20, had no significant difference, with 40 vs. 60% hatch in okra vs. standard leaf canopies. That variation and questions about the magnitude of effects on hatch rates prompted research trials on hatch rates under very high temperatures and low humidity in 2023.