By Travis J. Prochaska and Justin McMechan
Soybean gall midge was first described as a new soybean pest in Nebraska during the 2019 growing season. However, the 2023 growing season has presented several growers in the area with their first experience with the emerging pest, even as others in eastern Nebraska have been dealing with the pest for several years.
The first detection of an adult gall midge for the 2023 growing season was observed on May 26 near Mead. This is the earliest recorded date of adult emergence since the alert network started in 2019 (McMechan et al.). Typically, adults emerge in early to mid-June.
Overwintering adult soybean gall midge emerge from the previous year’s soybean fields and fly to an adjacent soybean field to lay eggs on young soybean plants. As the eggs hatch, the immature larvae feed on stem tissues underneath the epidermis, disrupting water and nutrient uptake within the plant. As the larvae grow, they will transition from a white to a bright orange color specimen.
Infested soybean plants can wilt or lodge at the feeding site and, in some cases, result in the death of the plant. Plants become susceptible to infestation around the vegetative V2 leaf stage as fissures (small cracks) develop near the base of the stem, providing an entry point for females to lay eggs.
Management has been hit-and-miss. Research studies completed by Nebraska Extension Crop Protection and Cropping Systems Specialist Dr. Justin McMechan’s lab have shown some results, but foliar-based treatments have been inconsistent between locations and years. Chemical control should only be considered if the history of gall midge has been recorded or an adjacent field has shown a history of gall midge. Gall midge is a field edge pest, so any treatments should be confined to the first 60-120 feet of the field.
Research has shown that hilling — a process where soil is used to cover the base of the stem — can be an effective strategy to control; however, it is difficult to implement at the V2 stage and not cover up the small soybean plants.
Granular at-plant applications with Thimet 20G have shown consistent control, but its use is limited due to the need for additional specialized equipment.
A multi-year field study funded by the Nebraska Soybean Board has shown that delaying soybean plantings until late May can reduce infestation and injury.
Studies led by Dr. Bob Koch, University of Minnesota, are showing some success with biological control and predators (i.e., ground beetles, parasitic wasps, etc.); however, further studies are needed to fully understand their impact.
As with any insect-related program, scouting will be key. Scout field edges of soybean that are adjacent to fields planted to soybean last year. Scouting should begin approximately two weeks after the first adult detection. To receive alert notifications of soybean gall midge adult emergence, go to soybeangallmidge.org and register for the alert network.
To assess a soybean plant for larval infestation, look for any dark brown or black discoloration near the base of the stem below the cotyledonary nodes. If found, peel back the outside layer of the stem to reveal any possible white or orange larvae.
As we approach September, there are no practical management tactics this late in the season. However, scouting to build a profile and a history will be helpful for possible treatments for the 2024 crop.
Funding for this project is supported by the Nebraska Soybean Board Checkoff.Source : unl.edu