Editor’s note: The following was written by Joseph Spencer, Kelly Estes and Nicholas Seiter with the University of Illinois for the university’s farmdoc daily website.
It’s not here yet, but there’s a new soybean pest approaching on the distant western horizon. Illinois entomologists were part of a project to survey for it in Illinois during the 2020 growing season.
Resseliella maxima, the soybean gall midge, is a newly identified pest capable of causing heavy damage in soybeans. Economic damage occurs when the bright orange larvae of the midge (a type of small fly) feed on the phloem and xylem (vascular tissues) at the base of soybean plants.
Plants that are not killed by an infestation are likely to experience reduced yield. Additional losses are possible due to lodging of weakened plants. Most heavy damage (complete yield loss) is confined to areas within 100 feet of field edges, with 20% yield loss possible within 200-400 feet of the field edges.
The soybean gall midge overwinters as a larva in the soil of the soybean field. They pupate and emerge as adults in June and July. Subsequent infestations are most likely on the edges of soybean fields that are adjacent to soybean fields that were infested during the previous year.
Adults are believed to lay eggs at the base of soybean plants. Early indications of an infestation may include discoloration of plant stems near the soil interface, while more advanced infestations may manifest as wilting or dead plants. Peeling back the epidermis of an infested stem will reveal the presence of bright orange larvae. There are multiple generations each year.
University of Nebraska data suggest that there is no single approach that will manage soybean gall midge.
Illinois had a surveying role in a large regional gall midge sampling project supported by checkoff funding through the North Central Soybean Research Program. The project, “Soybean Gall Midge: Surveying the North Central Region, Adult Monitoring and Host Plant Resistance,” was focused primarily on regions to our west where the pest was first discovered in 2018 and the expanding area of infested counties.
During 2020, infestations in 19 additional counties were documented, bringing the total number of infested counties to 114 across South Dakota, Nebraska, Minnesota, Iowa and Missouri. The nearest infestation to an Illinois border is more than 140 miles away in central Iowa.
The current distribution of infested counties is available at soybeangallmidge.org/.