By Andi Anderson
Illinois soybean growers face changing pest pressures as researchers continue tracking insects that threaten crops across the Midwest.
Two pests receive special attention soybean gall midge and dectes stem borer. Ongoing studies help farmers understand current risks and prepare for 2026.
Soybean gall midge remains a concern in neighboring states but has not been found in Illinois. After three years of statewide monitoring researchers confirm the pest is still absent. In 2025 surveys covered about 200 soybean fields across 45 counties.
Because adult gall midges are extremely small detection focuses on plant inspections rather than sweep nets. Researchers carefully examined soybean stems especially along field edges where early damage usually appears.
No soybean gall midge injury or larvae were detected. This finding provides reassurance but continued monitoring remains important.
Dectes stem borer presents a different situation. This insect is already established in Illinois and is becoming more important especially in southern regions.
Research led by scientists at the University of Illinois examined larval populations from 2021 through 2023 with special focus on no till and reduced till fields. These systems leave crop residue undisturbed creating ideal overwintering habitat for larvae.
In 2025, researchers focused on two known infestation sites in southern Illinois. Soybean residue was sampled throughout summer to follow larval development. Adult borers appeared in late June and remained active into mid-July.
This timing helps farmers plan scouting and management activities. Populations were most common in south central Illinois counties including Marion Franklin Jefferson and Washington.
Farmers are advised to begin scouting in late July or August after eggs are laid. Fields with more than 30 percent of plants infested should be harvested early to reduce lodging risk. Lodging occurs when larvae girdle stems before winter and can cause harvest losses.
This multi-year work supported by the Illinois Soybean Checkoff and a regional study funded by the NCSRP highlights the value of early monitoring. Staying informed helps growers protect yields and adapt management practices as pest threats evolve.
Photo Credit: gettyimages-zoran-zeremski
Categories: Illinois, Rural Lifestyle, Farm Safety