Systemic efficacy of the diamide insecticides targeting corn earworm (Helicoverpa zea) in Mississippi soybean production

Over the last five years, flubendiamide and chlorantraniliprole have become valuable management tools for lepidopteran pests in MS soybean production. These insecticides provide excellent residual control of lepidopteran insect pests and have been widely used since their introduction into the agricultural community. To determine if these insecticides are translocated to other parts of the plant, a series of experiments were conducted in the summers of 2013, 2014, and 2015 at Mississippi State University in Mississippi State, MS.  Flubendiamide and chlorantraniliprole were applied to soybean at the V4 and R3 growth stages to determine if they moved to new tissues as the plants developed. Ten upper most newly emerged trifoliates that were not exposed at the time of application and ten leaves from the treated portion of the canopy were removed from each plot to determine the systemic and residual efficacy of these insecticides. Leaves were removed at various intervals after application until 32, 31, and 28 days after treatment in 2013, 2014, and 2015, respectively. At R5.5, ten soybean pods were removed from each plot to determine if the insecticides moved to the seed and to the seed hull. Corn earworm, Helicoverpa zea (Boddie), larvae were placed on leaf material, seed, and seed hulls to test for presence of the insecticide. Mortality was evaluated three days after exposure. Larvae were deemed dead if they were unable to right themselves after being flipped onto their dorsal side. At 25 days after treatment, flubendiamide resulted in 90% mortality and chlorantraniliprole resulted in 98% mortality and the untreated control had 8 % mortality on leaves that were exposed at the time of application.   At 25 days after treatment, in leaves that were not present at the time of application, flubendiamide resulted in 10% mortality, chlorantraniliprole resulted in 90% mortality, and the untreated control resulted in 10% mortality. Neither insecticide was detected in the seed or seed hulls in this study. These results suggest that chlorantraniliprole moves to new vegetative structures but not to the reproductive structures of the plant and that the movement of flubendiamide was not observed in these studies.