Scouting Tips for Gall Midge in Soybeans

DECATUR, Ill. (DTN) -- The first soybean gall midge adults have fallen into the trap. Researchers involved in a multi-state monitoring network started spotting the pest in Nebraska last week, on June 7.

Farmers should begin scouting for gall midge larvae in the next two weeks in fields with a history of pressure, recommended University of Nebraska Crop Protection and Cropping Systems Specialist Justin McMechan.

Soybean gall midge adults may find fewer suitable early egg laying sites this year because of delayed planting. Soybean plants aren't considered susceptible until they reach the V2 growth stage.

This is a relatively new insect pest. It was identified as a problem in 2018 and has since been documented in 140 counties spread between Nebraska, Iowa, Missouri, South Dakota and Minnesota. In 2021, it was identified in 26 new counties; three of those had larval presence only on sweet clover.

Fortunately for farmers, scientists from those states have teamed up to aggressively research and track the pest. So far this year, discoveries have been in Davey, Mead, Syracuse, Memphis, Springfield and Weeping Water, Nebraska. Farmers can find detailed scouting videos and in-depth information about the soybean gall midge at https://soybeangallmidge.org/….

CONTROLS NOT CONSISTENT

McMechan said management of soybean gall midge remains difficult, although much has been learned about the pest. Since the insect was new to scientists, there was a laundry list of things to discover about how the insect is distributed across the landscape and how it behaves to learn how to scout for it. Cultural, biological and host plant resistant tactics are also being explored.

What's known so far is that initial infestations typically occur in June with multiple generations during the summer. The midge life cycle includes overwintering in the soil as larvae in silken cocoons. The adults that emerge in June primarily infest field edges adjacent to fields that were infected the prior year.

Adults lay their eggs in the soybean stem and the larvae feed under the epidermis, reducing water and nutrient movement -- causing the plant to wilt and die. The worst damage tends to be in the outside 50 to 100 feet of the field that is next to a field that was planted to soybeans the previous year.

Chemical controls have shown some results. But foliar sprays also tend to be inconsistent between locations and years. Research has not found a specific foliar product that has provided consistent control of soybean gall midge, McMechan said.

After the most recent adult discovery in Nebraska, the scientific working group issued a release stating that research to date suggests growers can consider using a combination product that contains a pyrethroid. However, it was also stated that if a control application is being considered, it should only be made in soybean fields where a history of soybean gall midge injury has occurred.

The alert reads: "Since soybean gall midge is a field edge infesting pest, growers may only need to treat the first 60 to 120 feet of a field edge that is directly adjacent to a field that was injured the previous year. Do not treat any soybean fields prior to V2 as they are not susceptible to infestation due to the lack of fissures or cracks at the base of the stem."

BUILD A HILL?

The alert also issued a suggestion on the possible use of hilling as a control strategy: "Hilling or covering the base of soybean stems with soil has also been found to be a very effective strategy with almost complete control of soybean gall midge. This is a difficult practice to implement when soybean plants are small as they can easily be completely covered by soil. Studies are being conducted to evaluate the timing of hilling relative to the plant development stage. Little is known about the impact this management strategy could have on soybean gall midge movement in a field. Although no field studies have been conducted, it is possible that adults may continue to move into the field until they find a susceptible plant."

Recent hail events could make soybean plants more open to egg laying, McMechan told DTN. "We've done those studies and gall midge adults will infest areas where wounding occurs.

"The larval population per plant can also increase. However, I think it might be more important with late-season hail events," he said.

Farmers are unlikely to spot the adult version of soybean gall midge as they are extremely small. It is the larvae that hatch and feed within the soybean stem that are visible during scouting.

SCOUTING TIPS

The following are some scouting tips:

-- Scout edges of soybean fields adjacent to fields that were in soybeans the previous year, especially if they had a gall midge infestation.

-- Focus on fields that are V2 or older -- that's when the soybean stem starts to crack along the surface near the soil line. The adult lays eggs in these stretch marks or fissures.

-- Look for dark brown or black discoloration of the base of the stem. Scrape the exterior layer of the stem away to reveal larvae that start white and turn orange as they mature.

You can set up an alert notification of gall midge discovery at https://soybeangallmidge.org/….

Pamela Smith can be reached at pamela.smith@dtn.com

Follow her on Twitter @PamSmithDTN

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