We have heard a few reports of either bean leaf beetles, grasshoppers, or stink bugs increasing in soybeans. As we start to approach the end of the growing season the larger concern with these insects is the potential for pod feeding, rather than foliage feeding. Pod feeding directly impacts grain quality. Crop stage is also an important consideration. Late-planted fields or double-cropped soybeans which are still green when other fields are drying down can be “trap crops,” attracting the insects that are leaving the other maturing fields. Such fields bear close watching.
Evaluation of pod chewing injury should be based on inspection of all pods on 10 randomly selected plants. Be sure to sample at least 100’ into the field to avoid making your entire decision based on field edges, where damage can be worse than in the field as a whole. On each plant sampled, count the number of total pods and the number of pods exhibiting pod injury, and then determine the percent pod injury based on the 10 plants inspected. It is important to estimate percent pod injury on inspection of the entire plant. Treatment is justified if the percent pod injury approaches 10 to 15%, and beetle adults or grasshoppers are still present and active in the field.
Stink bug feeding on pods is more subtle because they insert their straw-like mouthparts directly into the developing seed and you will not see chewing damage. Beans will be vulnerable to this type of feeding through the end of the R6 growth stage (full seed). To look for stinkbugs, take a set of 10 sweeps in 10 different areas of the field (although stink bugs are mostly found along the edges, they can also be found in the interior of the field). If the average number of stink bugs is higher than 4 per set of 10 sweeps, treatment is necessary (this decreases to 2 per set of 10 sweeps if soybean is grown for seed or food grade). Visit our website for more information on stink bugs in soybean, including helpful guides for identification aginsects.osu.edu
When making a treatment decision, keep in mind the pre-harvest interval of the insecticide you’re considering – which can be an important factor at the end of the season as harvest approaches. For an up to date listing of insecticides used in soybean including pre-harvest intervals and labeled insect targets, visit the soybean chapter in our new Insect IPM Guide https://aginsects.osu.edu/news/msu-osu-insect-ipm-guide.
For more information about bean leaf beetle visit our factsheet at https://ohioline.osu.edu/factsheet/ENT-23.