Soybean Gall Midge
The soybean gall midge was recently (2019) described as a new species, Resseliella maxima. Midges belong to a large and diverse family of flies — there are over 1000 species of midges in North America. Some midges are economically important plant pests; others are predatory on aphids and mites. Some midges form abnormal growths, called galls, as they feed.
Midge infestations are not unknown in soybean fields, but were previously assumed to be a secondary infestation after some kind of injury such as hail or disease. However, in 2018 and 2019, gall midge infestations have been observed earlier, in higher numbers, and often in the absence of injury or disease.
Gall midge biology, agronomic impact, and management are currently active areas of research in the north-central region.
Feeding by soybean gall midge larvae causes injury to the lower soybean stem, leading to wilting and whole plant death. Surviving plants with weakened soybean stems are susceptible to breaking.
Gall midge infestations are usually concentrated along field borders where losses can be 90-100%. Studies are underway to determine the economic impact of this new pest.
Soybean gall midge overwinters as larvae in the first few inches of soil. After pupation in the early spring, adult midges emerge and lay their eggs at the base or lower stems of soybean plants.
The eggs hatch and the larvae feed on the stems. Infestation does not occur until after the V3 stage, and can continue into the reproductive growth stages. The adult gall midge does not feed on soybeans.
It is not yet known if there are two or three generations per year in the north-central region of the U.S.
Wilting or dead soybeans along field edges with decreasing damage into the center of the field is usually the first sign of infestation. The heaviest infestations have been observed in fields next to a field that had been planted to soybean in the previous year.
After the V3 stage, check soybean plants at the field edge for small white to orange larvae of the gall midge. See a scouting video here. The presence of small, orange larvae in the base of a soybean stem is considered diagnostic for this pest.
To date, the gall midge has been found and identified in Nebraska, Iowa, Minnesota, and South Dakota. It is not known if the soybean gall midge will persist in areas where it caused economic losses in previous years or if it will spread to other areas.
Because this is a very new pest, there are not yet any research-based management recommendations. Checkoff funding is supporting on-farm studies in multiple states on the efficacy of cultural practices and insecticides on injury due to gall midge feeding.
To date, seed treatments have not been effective. It appears that later-planted soybean have lower infestation rates.