Source: Soybean Gall Midge Alert Network
Figure 1. Counties with soybean gall midge detection in 2018 – 2023.
163 counties have been documented as infested as of 10/23/2023. 8 new counties.
- Plants are most susceptible to soybean gall midge (SGM) at the V2 stage and beyond, exhibiting symptoms of wilting around 20 days post adult emergence.
- There are no known “sure fire” management techniques, but mitigation measures such as mowing densely vegetated field edges, spring tillage, late planting and insecticides (foliar and seed treatments) can help lessen impact.
Figure 2. Adult female SGM. Source: A.J. McMechan. University of Nebraska-Licoln. 
Figure 3. Soybean gall midge life cycle.Introduction
There is a vast amount of research taking place on SGM but large gaps in knowledge remain due to the recent discovery of this new pest. Although it can’t be confirmed, orange larvae suspected to be SGM were first observed in a field in northeast Nebraska in 2011. Since 2018, larval detection of SGM have been detected in 155 counties in 5 states in the mid-west (Figure 1). In 2019, SGM was described as a new species in the insect Order Diptera (True Flies: Family Cecidomyiidae (Gall Flies) as Resseliella maxima Gagne (Figure 2). Soybean is the most studied host; however, sweet clover, alfalfa, dry bean and lima bean are other known hosts.
Life Cycle and Feeding
SGM adult activity is continuous throughout the growing season after first adult detection making it difficult to determine the number of generations per year. Field collected data on adult emergence from overwintering (previous season soybean) and the current season soybean fields indicates that the generation time is approximately 30 days (Figure 3). The life cycle begins in the soil when the overwintering 3rd instar larvae (Figure 4b) in silken cocoons pupate in the spring and subsequently emerge as adults in early- to mid-June. After mating, females lay eggs in natural cracks and crevices at the base of soybean plants below the cotyledonary nodes. The eggs hatch and the first larval stage feed within the stem towards the base of the plant. SGM have a total of three instars; the 1st and 2nd are whiteish colored and small and the 3rd instar is bright orange and comparatively large (Figure 4). These orange larvae then fall off the plant and pupate in the soil. After the transformation to adult is complete, they emerge and repeat this cycle.
Figure 4. Field view diagram. Source: Justin McMechan, University of Nebraska-Lincoln. (a) 3rd instar larvae are orange; (b) 1st and 2nd instar larvae are white; (c) sporadic feeding damage (dead plants) in a field.Scouting Considerations:
- Confirmed hosts of SGM include alfalfa, sweet clover, dry bean, and lima bean.
- SGM are observed to work their way in from field edges which are often the hardest hit field areas.
- Plants are most susceptible at the V2 stage or later (cracks and fissures in the ground may be necessary for egg laying).
- Wilted plants and darkened stems (at ground level) are the most notable symptoms (Figures 4c and 5).
- Split the soybean stem and look under the stem epidermis to look for larvae (Figure 4a).
Figure 5. Stem expansion – stretch marks and tissue damage.Management
Information gathered from University and Industry research in 2019 and 2022 has revealed key points:
- Duration of adult emergence ranges from 3-45 days and this is the stage to target with foliar insecticides. Every 28-32 days there may be new flushes of adults from either the over wintering population or in-season generations.
- Infestation by SGM appears to take place around the V2 soybean growth stage.
- Monitoring SGM adult activities utilizing adult emergence cages as part of an emergence network across NE, IA, SD and MN with activity reported on www.soybeangallmidge.org.
- Planting date can have a significant effect on infestation, when planting occurs after May 22, however, more data is needed to determine the stability of this tactic.
- Fall and spring tillage have not been consistent with some site-years showing little to no effect from tillage.
- Mowing dense vegetation around fields had a slight effect on infestation.
- Utilization of a seed treatment with an insecticide had some effect but results have been inconsistent between sites and years. Evaluation of insecticidal seed treatments remains ongoing.
- Foliar applications of a pyrethroid like Warrior II with Zeon Technology® or pyrethroid containing Endigo® ZC showed some efficacy up to 11 days after first adult emergence but has not been consistent.
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