Supplemental control with diamides for Heliothines1 in Bt Cotton

Authors: Little, Nathan; CATCHOT, ANGUS - Mississippi State University; Allen, Clint; GORE, JEFFREY - Mississippi State University; MUSSER, FRED - Mississippi State University; COOK, DON - Mississippi State University; Luttrell, Randall

Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2017
Publication Date: 3/1/2017
Citation: Little, N., Catchot, A.L., Allen, K.C., Gore, J., Musser, F.R., Cook, D.R., Luttrell, R.G. 2017. Supplemental control with diamides for Heliothines1 in Bt Cotton. Southwestern Entomologist. 42(1):15-26. doi:10.3958/059.042.0102.

Interpretive Summary: In this manuscript, we investigated the benefit of supplemental control of bollworms in Bt cotton with a new class of insecticides, the diamides. This study was conducted across 2014 and 2015 in the Mississippi Delta with a total of 14 replicates at seven different locations. No substantial differences in yield or net profits were found among sprayed or unsprayed Bt cotton in this study. However, the lack of increase in net profit for untreated Bt cotton and a trend for higher numerical net profit in sprayed Bt cotton challenge pest management recommendations to avoid oversprays in cotton whenever possible. Data from this study should provide some confidence for producers to avoid oversprays at near threshold densities of bollworms in Bt cotton.

Technical Abstract: Supplemental control of bollworm, Helicoverpa zea (Boddie), in Bt cotton with diamides is becoming more frequent, but there is little information on the net returns to growers. Seven locations were established across the MS Delta cropping region between 2014 and 2015 to examine the value of spraying Bt cotton with commercially available diamides. Bollgard II®, Widestrike 3®, and non-Bt cotton varieties were planted at each location, and divided into five subplots. The following treatments were randomly assigned to the subplots within each cotton cultivar: 1) lowest labeled rate of chlorantraniliprole applied at threshold, 2) lowest labeled rate of flubendiamide applied at threshold, 3) lowest labeled rate of '-cyhalothrin + chlorantraniliprole applied at threshold, 4) a sprayed control, which was the maximum labeled rate of chlorantraniliprole applied on a three week schedule and initiated prior to first bloom to minimize damage from heliothines, and 5) an untreated control. Plots were scouted weekly for larval abundance and plant damage by examining 100 plants chosen at random in each plot. Supplemental control applications were initiated when larval densities (>4 per 100 plants) and plant damage (>2 damaged bolls with larvae present) met economic thresholds outlined by the Mississippi State University Extension Service for larval densities and damaged fruit. Following first bloom, all non-target pests were controlled with broadcast sprays of insecticides with low or no known toxicity to heliothines. No differences were detected in yield among treatments within any given Bt cotton variety. Non-Bt cotton required approximately one additional diamide application on average for heliothine control as compared to Bt cotton plots. Results from this study indicate that there was no economic benefit to supplemental sprays of diamides for bollworms in Bt cotton at the larval densities observed during this study. Bt cotton alone appeared to be sufficient for control of bollworms. This should provide some confidence for producers to avoid oversprays at near threshold densities of bollworms.