GRAND FORKS, N.D. — Few people in Upper Midwest had even heard of soybean gall midges until a few years ago, but now the insect is a growing threat to soybeans in the region.
"This is an economically important insect that we're concerned about," said Janet Knodel, North Dakota State University Extension entomologist.
The insects can cause significant damage to soybean fields when the pests feed and lodge in plant stems. Yield loses can range from 20% to 100% on field edges, where damage is most common, she and other experts say.
Knodel spoke Feb. 20 in Grand Forks at the annual International Crop Expo, of which soybean groups are among the organizers.
Though the species wasn't identified until 2018, the insects were first documented in Nebraska in 2011 and have been spreading north since then. Species identification is highly specialized, which slowed initial work on the insect, Knodel said.
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Today, the insect also has been identified in Minnesota, North Dakota and South Dakota. "It just continues to slowly spread," Knodel said.
Soybean gall midge is one of 15 midges in the United States and the first to affect soybeans. Other members of the midge family include Hessian fly and wheat midge, which are pests in wheat. Soybean gall midges are "tiny, about a quarter of an inch and have striping on the legs and mottled wings," Knodel said.
Adult soybean gall midges lay eggs in the soil near the soybean plant stem or in the stem itself. When the eggs hatch, the larvae begin feeding on the stem, causing the plant to wilt and die. The "gall" in the insect name refers to the formation of an enlarged area on the stem where the larvae feed.
The adult insects are weak flyers, so most of the damage they cause is on the edges of fields, Knodel said.
The following suggestions can help to identify fields infested with the insect, according to information from NDSU:
- Scout earliest planted fields first.
- Look for dark discoloration at base of stem.
- Peel back stem epidermis and look for larvae.
Research now underway will help to provide more information on how to manage the insects in a soybean field.
Because the insect is relatively new, farmers may need help to identify it if they suspect it's in their fields, Knodel said.
"Please, if you find anything send it to me or your county extension agent," Knodel said. She can be contacted at janet.knodel@ndsu.edu.
