August’s Stealthiest Insect Pest: Stink Bugs in Soybean

By Kelley Tilmon and Andy Michel

Why are stink bugs the stealthiest insect pest near the end of summer?  It’s because their method of feeding is so subtle.  You won’t see damaged leaves or sickly-looking plants with stink bugs.  They have straw-like mouthparts which they poke through the pod directly into the developing seed.  If this happens early enough in seed development the seed will simply abort.  If it happens later, the seed will be shriveled and shrunken.  Either way, this reduces yield and/or reduces seed quality, though you will not see the damage unless you carefully inspect the pods for missing or damaged seed.

The good news is that soybeans are relatively easy to scout and are susceptible to the insecticides labeled for them.  There are many species of stink bugs that feed on soybean including brown marmorated stink bug (BMSB), green, red shouldered, and brown stink bugs. It’s not necessary to distinguish between them for threshold purposes. 

Begin scouting for stink bugs when the soybean plant reaches the R2 stage (full bloom, when the plant has an open flower at one of the two upper-most nodes on the main stem). Stink bug feeding can cause economic loss from the R3 stage (pod set) to the R6 stage (full seed set).  Using a sweep net, sample in at least 5 locations in smaller fields, more in larger fields. Stink bugs tend to be more numerous on field edges so sample throughout the field for the overall picture. At each location take a set of 10 sweeps, taking a step with each sweep of the vegetation. Count the number of stink bugs captured in your sweep net for each 10 sweep set. All pest stink bug species, both adults and nymphs, should be counted together.  In soybeans grown for grain the threshold is 4 bugs per 10-sweep.  In soybeans for seed or food the threshold is 2 bugs per 10-sweep (because the reduction in seed quality is more important). 

For more information about stink bug biology, identification, and management visit our field guide to the Stink Bugs of Ohio Soybean here.