Soybean gall midge has been observed in North Central region soybean-producing states for the past 10 years. For instance, isolated soybean fields in northeast Nebraska had SGM in 2011.

At that time, the orange maggots were found on hail-damaged plants, feeding on the decaying tissue. Fast-forward to June last year, when reports started coming in from Nebraska, South Dakota, North Dakota, Minnesota and Iowa fields with visible signs of dead or dying plants, with symptoms associated with SGM.

Where feeding was most prominent, white-to-orange larvae were found on darkened areas of the plants along field edges, with decreasing damage farther to the interior of the fields.

Plant death seemed to be worst along waterways and ditches with dense vegetation such as brome grass. Plus, heavily infested fields often were next to a field that had been planted with soybeans the previous year.

This suggests to Nebraska Extension entomologists such as Justin McMechan that SGM might have overwintered in the last year’s soybean fields and moved to areas of high humidity before entering fields last season. Infestations occurred last season in early June, about two months earlier than previous infestations.

When Nebraska researchers surveyed producers about SGM damage, they found that infested fields had an average of 77% yield loss in the first 100 feet of those fields and averaged 17% yield loss in the rest of the field, with some extreme cases up to 30% yield loss.

“Producers have told us that they have seen on and off pressure from the midge prior to last season,” McMechan says. “We often thought that the orange maggots were a secondary pest that was opportunistic, taking advantage of previous disease and mechanical damage.”

But McMechan acknowledges that 2018 was an entirely different type of year.

“At first, we just saw localized reports that were coming into the University of Nebraska and Iowa State University diagnostic labs for disease damage,” he says. “But on about 20% of the samples sent in, there was no plant disease found. Those results combined with distribution of damage in the field gave us the heads-up that it could be an insect issue.”

Conducting producer surveys across the southern counties in Nebraska, and north to Haskell Ag Lab at Concord, Neb., researchers found SGM everywhere.

“We captured adult midges in August last year,” McMechan says. “We had never seen them before, so we finally had the opportunity to identify the species.”

Worldwide, 55 species of the genus Resseliella previously had been identified, with 15 of those species observed in the U.S. Thanks to researchers in the U.S. and Japan, SGM found in Nebraska and surrounding states now has been identified as an entirely new species, with little genetic overlap common to known species.

“In that genus, we don’t have a ton of them that are major agriculture pests,” McMechan says. “There is another midge in Japan that also feeds on soybeans, but it is a different species than the ones we are seeing.”

That makes it more challenging for researchers and farmers to manage this new pest.

“The fact that this is a new species tells us that we have a lot of work to do,” McMechan says. “Our current management decisions are lacking knowledge of the biology and ecology of this species. Because we have so much to learn, we want to work with producers to understand SGM, so we can get to some effective management practices.”

It is likely that SGM is overwintering in soybean fields, so regional soybean-producing states are joining forces to monitor when SGM adults emerge this spring, when they lay eggs and how long they lay eggs.

“If we can understand these things, we get to the cultural control tactics like tillage and planting dates,” McMechan says. “From a treatment standpoint, we are probably looking at a spring insecticide application, but how far into the field that application is done and how planting dates play a role are still things we don’t know.”

McMechan says researchers will be monitoring SGM this season to observe how quickly the pests mate after emergence and when they begin infesting soybean fields.

“We know they are poor flyers, but it’s likely that winds can move them around,” he says. “And everything we know about them is taken from another species.”

At Eastern Nebraska Research and Extension Center near Mead, researchers are trying to develop a colony of SGM so they can study them year-round to observe the species and evaluate more chemistries.

“If the pressure is high this season, we will learn much more and be able to develop management strategies quicker,” McMechan says.

Learn more by contacting McMechan at [email protected].