Stink Bugs on Soybean in the North Central Region (2017) is a cooperative effort of land-grant universities in the midwest, the USDA, and the North Central Soybean Research Program, with checkoff funding provided by NCSRP.
Stink bugs are relatively large insects, from 1/2 to 1-inch long as adults, with a characteristic "shield" shape. Stink bugs are attracted to soybean plants in the bloom to early pod-fill stages and use their piercing and sucking mouthparts to feed on developing seed.
There are several species of stink bugs common in northern soybeans including the green stink bug and brown stink bug. Several other species of stink bug are found in southern states and may be moving north. These include the redshouldered stink bug, the redbanded stink bug, and most recently, the brown marmorated stink bug, an invasive species making its way across the continent.
Two beneficial stink bugs may also be encountered in soybean: the spinedshouldered stink bug and the twospotted stink bug. These stink bugs are predators of crop pests and should not be included in calculations for monitoring and treatment.
A new field guide, Stink Bugs on Soybean in the North Central Region, is available to assist growers and scouts identify and monitor stink bugs and their damage in the North Central region.
For a detailed review of stink bug biology and management, see the publication Identification, Biology, Impacts, and Management of Stink Bugs of Soybean and Corn in the Midwestern United States, Journal of Integrated Pest Management, 2017.
Immature stink bugs are called nymphs, and look similar to adults
Photo: University of illinois Extension
Both nymphs and adults are attracted to developing seed in maturing soybean fields. They will also feed on soybean stems, foliage and flowers. Direct feeding mainly reduces soybean quality. Young seed can become deformed or remain undersized; older seed discolored or shriveled. The feeding wound provides an entry for secondary diseases, and affected seed more likely to deteriorate in storage.
Stink bugs prefer soybean, but will also feed on developing fruit, fruit trees, corn and other crops. Stink bugs cannot clip silks in corn, however, as they do not have chewing mouthparts.
Stink bugs overwinter as adults or older nymphs in protected wooded areas beneath leaf litter or logs. Most stink bugs in the upper midwest have probably migrated from overwintering sites further south. Stink bugs go through a simple metamorphosis with egg, nymph, and adult stages. After hatching, the wingless nymphs molt several times before becoming full-sized, winged adults. There is usually one generation per year in the north.
During early summer, stink bugs feed on berries, pods, and seeds in uncultivated, wooded areas, and move to crops as seed and fruit mature.
Spined soldier bug nymph Photo credit: R. Ottens, Univ. of Georgia
Because female stink bugs are highly attracted to the soybean plant once it starts to bloom, sampling should begin at that time. Counts the number of older nymphs (larger than 1/4 inch) as well as the adults.
Use sweep nets or shake plants over a drop cloth. Sweeps are more appropriate for drilled, narrow row beans. A “shake sample” to dislodge bugs from the canopy on to a light colored cloth placed between rows is suitable for wide row beans.
Stink bugs aggregate, and it’s more common to find them at field edges or in groups on plants in localized spots, rather than in the middle of a field or distributed throughout a field. Therefore, check 5 different areas of the field; for example, 20 sweep net samples at each of 5 locations. Calculate stinkbugs per sweep (or per row foot) based on the whole field, and not an infested clump at one field edge or corner.
Stink bug thresholds range from 1 to 3 bugs per foot of row as soybean pods begin to fill. Check with your state Extension entomologist for the recommended threshold in your area. Because stink bugs usually reduce quality more than they do quantity; soybean grading standards are helpful to determine the need for rescue insecticide treatments. Thresholds would also be higher for seed beans than grain soybean.
Stink bug populations are partially suppressed by predators and parasitic wasps. The egg parasitoid Telenomus podisi is a common parasitoid that can significantly reduce the number of stink bug eggs in a field. Parasitized stink bug eggs are typically darker than nonparasitized ones.