By Christian Krupke and John Obermeyer
- Southern Indiana field surveys reveal larger-than-usual green stink bug populations.
- Scouting is necessary, as numbers vary within and between fields.
- Stink bugs feed by sucking fluids from developing seed, although it takes large numbers to cause economic damage.
For the last couple of years, we’ve had reports of noticeable populations of green stink bug in southwestern Indiana soybean fields. Some suspected damaged pods were sent to the Purdue Plant and Pest Diagnostic Lab for analysis during soybean harvest. Unfortunately, there was never conclusive evidence that stink bugs had damaged the pods and reduced seed size, e.g., reduced yield. This week, Larry Bledsoe, Entomology Field Research, sampled some southern Indiana soybean fields for an unrelated insect. However, what he found in a few fields at R5 growth stage, were large numbers of green stink bugs. He did emphasize that there was tremendous variability between fields. Although stink bugs are a key pest of soybeans in the southern US and South America, we don’t generally have treatable infestations this far north.
The green stink bug,a native of North America, is a flattened, shield-shaped bug, so named because of the offensive odor it produces. The adult is bright green and about 2/3 inch long. It is easily distinguished by the triangular-shaped plate that partially covers its wings and the characteristic foul odor they give off when handled. The nymphs hatch from clusters of barrel-shaped eggs. They closely resemble the adults throughout their several nymphal stages. The nymphs, however, are wingless, black and red in color, and lack the triangular plate. Green stink bug may appear in soybean fields from mid July through harvest time. Often they are most numerous in the border rows next to weedy or wooded areas; border sprays are a suitable option for control in many cases.
Green stink bug feeding on pod.
Stink bug damage to seed.
Both green stink bug adults and nymphs feed using their piercing-sucking mouthparts. They cause injury to soybean by puncturing pods and sucking fluid from the developing beans. This feeding also introduces bacteria, fungi and yeasts that may cause further damage. Seeds that do develop despite stink bug pod feeding may be smaller, shriveled, and/or discolored. This damage may lower bean quality, and ultimately reduce yields.
If stink bugs are found in a field after the pods have begun to form, take 20 sweeps with a sweep net in each of 5 field areas. Determine the average number of bugs per sweep. Control may be necessary if there are 40 stink bugs per 100 sweeps (0.4 bugs/sweep) and pods are still green.