GALL MIDGE MOVES SLOWLY, BUT SURELY, EAST

DR. CHRIS DIFONZO MSU PROFESSOR & FIELD CROPS ENTOMOLOGIST

One of the most frustrating soybean pests to emerge this century is the soybean gall midge. After 100+ years of large-scale corn and soybean production in the U.S., most new pests are species introduced from abroad, for example the soybean aphid and brown marmorated stink bug from Asia. Occasionally, a native pest expands its range; western bean cutworm comes to mind. But it is rare for a localized native insect to suddenly ‘become’ a crop pest. The soybean gall midge apparently did just that. After a few years of scattered reports in soybeans, it had a broader outbreak in several western states in 2018 and has been spreading ever since. A specialist determined that the midge was a new, unknown species existing nowhere else. Much of its origin and biology are still a mystery.

Midge larvae injure soybean plants by feeding on the stems, often near the soil line (A). The feeding not only cuts off water and nutrient movement, but allows pathogens to enter wounds. Besides stem damage, plants can wilt, lodge or die (B). The adult midges are tiny delicate flies which can’t fly very far after they emerge in June, thus infestations usually start on field margins closest to last year’s soybean ground. Egg laying and larval feeding can start in the early V-stages. Yield loss can be high, particularly on field edges (C), but management options are limited so far.

Gall midge is currently reported in 155 counties in the U.S., west of a line roughly from the Twin Cities south to Des Moines, Iowa. This puts it 340 miles due west of Ludington (in Rice County, MN) or the southwest tip of Michigan (in the Des Moines area). To date its spread is slow, moving a few counties to the east each season. But this does not rule out the possibility of farther spread due to weather fronts, or the possibility that low level infestations get missed where people aren’t looking. So when scouting soybean fields in the summer, be aware of what is happening on field edges and be curious if you see wilted or dead plants that aren’t associated with spider mites. It’s unlikely that gall midge would be found in Michigan before detection in Wisconsin or Illinois, but you never know!

The University of Nebraska oversees the Soybean Gall Midge Alert Network, a one-stop-shop for a current distribution map, scouting and management information, plus pictures and videos to aid in scouting and identification. You can also sign up for cell phone alerts of adult and larval emergence in the western states. The network is sponsored in part by the North Central Soybean Research program, and thus your checkoff dollars are at work. Visit https://soybeangallmidge.org to learn more.