Counties with Soybean Gall Midge Detection in 2018/2019, Soybean Gall Midge Adult Emergence Alert Network
Since the massive increase of Soybean Gall Midge (SGM) infestations in 2018, the spread of this newly identified species of true fly has not slowed. The 2019 growing season saw many fields fall victim to an outbreak of SGM that had otherwise remained untouched, which provides ample reason to predict a rather critical year in monitoring the spread of the insect throughout the Midwest.
Geographic Distribution
SGM has been reported and confirmed in 95 counties across 5 states as of 2019. Infestations have primarily occurred in eastern NE, eastern SD and western IA, and they have spread most recently into southwestern MN and surrounding areas.
Life and Feeding Cycle
- During third instar, larvae overwinter in the soil and emerge as adults the following spring.
- Adults mate and lay eggs at the base of soybean roots.
- Around 9 days after adult emergence, first and second instar larvae begin to feed on the roots and vascular system, causing structural damage to the plant and disrupting nutrient and moisture flow.
- Around 12 days after adult emergence, larvae transition to third instar.
- Around 20 days after adult emergence, infected plants begin wilting.
Field View Diagram: University of Nebraska-Lincoln, Justin McMechan
(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 and native lead plant.
- SGM are observed to work their way in from field edges; those areas are often the hardest hit.
- Plants are most susceptible at the V3 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.
Management
While there is no tried and true way to manage SGM at this time, there are measures that can be taken to reduce their impact, especially on high-pressure fields:
- Mowing densely vegetated field borders before adults emerge was proven in one trial to reduce infestation by 50%.
- Spring tillage has been shown to slightly reduce the emergence of overwintering adults.
- A seed treatment with an insecticide may reduce infestation, but more data is needed.
- High-risk fields should be planted last to potentially stall soybean growth enough to no longer align with adult emergence and egg laying.
- Apply a foliar insecticide (pyrethroid) at V3 if SGM adults are active in the field.
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