Efficacy of foliar insecticides for Dectes stem borer (Coleoptera: Cerambycidae) management in South Dakota soybeans

Dectes stem borer, Dectes texanus LeConte, is an insect that infests sunflowers, Helianthus annuus L., and soybeans, Glycine max L., in South Dakota. Historically Dectes stem borer has been a minor pest of soybean but has become increasingly prevalent in the southeastern area of the state since 2017. Most of the damage caused by this insect occurs when the larvae girdle the stem, leading to lodging. Lodging causes additional yield losses above the 10% to 15% reduction caused by larval tunneling activity. If detected, losses due to lodging can be minimized by early harvest of the infested field. Previous management recommendations proposed crop rotation and tillage as methods to minimize Dectes stem borer damage. However, these cultural strategies are not currently effective as Dectes stem borer populations continue to increase even when they are implemented. Previous research has determined that chemical management of Dectes stem borer is either not effective or cost prohibitive. This is due to the prolonged emergence period of the adult beetle and the larva being sheltered within the stem. The purpose of this research was to determine if timed insecticide applications can be used to effectively reduce Dectes stem borer pressure and improve soybean yields. This study evaluated several insecticides and three insecticide application timings. The results of the study indicate that calendar date applications will not be sufficient for the management of Dectes stem borer. However, when the applications synchronized with adult activity, we observed significantly fewer infested soybeans and improved yield.