As soybeans set seed and fill out, they need protection from pod-feeding stinkbugs. Several species will attack soybean, including the green, southern green and brown stinkbug. Adult stinkbugs are shield-shaped with a large triangular scutellum near the shoulder region. They are brown or green and are about 3/8 to 5/8 inches long.
Stinkbug eggs are barrel-shaped and laid in clusters of 25-100, mostly on the underside of leaves. Eggs may be yellow, white or green but will turn to pink or darker as the developing nymphs become ready to hatch. Nymphs vary in color, depending on their age and species. Some are quite colorful, with black, white and pink markings on their body.
Stinkbugs damage stems and pods with piercing-sucking mouthparts, sucking the juices out of the pods, and cause pod drop, yield loss and reduced seed quality. Damage from stinkbug can be similar to damage from drought, so make sure to sample and confirm the presence of stinkbug in the field.
Soybean fields planted in rows can be scouted by shaking plants over a drop cloth. The plant-shaking method works best after the beans reach one foot in height. A drop cloth consists of a piece of cloth (white or dark) measuring 24″ x 42″. Each end of the cloth is stapled to a thin strip of wood, approximately 1/2″ to 1″ wide and 24″ long.
To begin the survey, randomly select a site in the field, kneel between the two rows, and unroll the cloth from one row over to the opposite row. Extend each arm forward parallel with the row on either side and vigorously shake the vines over the cloth. Your arms, from your elbows to your fingertips, will allow you to sample approximately 1 1/2 row-feet of plants on each side of the row. Thus, three row-feet may be sampled at each site.
Count the insects that fall to the cloth. Repeat this process for 10 sites per 50 acres. Infestations are characterized as to the number of stinkbugs per 30 row-feet.
Sweep nets can also be used to scout for stinkbugs in soybean. Make 10 consecutive sweeps (swinging the net from side to side 180 degrees across the body, one swing per step) with a standard 15-inch diameter sweep net while walking through the field. After 10 successive sweeps, remove the insects from the net, identify and count them. Repeat this procedure 5 times for 50 sweeps and compare counts with suggested economic thresholds.
The thresholds for stinkbugs during pod set and pod fill are as follows:
- Drop Cloth: 1 stinkbug per foot of row
- Sweep net: 1-2 stinkbugs per sweep
There are numerous insecticides registered for stinkbug control. Control suggestions are listed in CR-7167 or page 320 in E-832, 2019 OSU Extension Agents’ Handbook of Insect, Plant Disease and Weed Control.