Soybean gall midge: Evaluating the efficacy of insecticide timing relative to adult emergence

Soybean gall midge (SGM) Resseliella maxima Gagné was recently identified as a new species injuring soybean in Nebraska, Iowa, South Dakota, Minnesota, and Missouri. SGM injury is caused by its three larval instars that feed on tissues within the soybean stem. Infested plants exhibit a darkening of the stem and nutrient disruption that can lead to wilting and death of plants. Yield losses of up to 100% have been reported in the field edge of SGM infested fields, with losses of 17-31% further into the field. Adult trapping methods for SGM have shown potential to assist clientele with the timing of insecticide applications. Unfortunately, no information exists on how the timing of these treatments could impact efficacy against SGM. An experiment was conducted near Memphis, NE to evaluate the efficacy of three different insecticides (Hero (bifenthrin and zeta cypermethrin; pyrethroid), Belay (clothianidin; neonicotinoid), and Dimethoate LV-4 (dimethoate; organophosphate) applied to separate plots at three different times (same day as emergence is detected, 5 days after, and 10 days after emergence is detected). To determine the effect of insecticide chemistry and timing, the plots are being evaluated for the frequency of infested plants, the number of larvae per plant, and rated on a categorical scale for plant injury. Statistics will be used to determine significant differences between insecticides and application times. This is the first study conducted on SGM insecticide timing and the results will assist farmers on potential window for insecticide applications to control SGM.