Late-Season Soybeans Can Be Pest Magnets

By Kelley Tilmon and Andy Michel

At the end of the growing season, when many soybean fields are shutting down, those which are still green can be a magnet for certain insect pests as they leave the mature fields.  Double-crop soybeans and late planted beans that are running behind and are still fresh can be attractive for stink bugs, bean leaf beetles, and sometimes grasshoppers when they leave yellowing fields for greener pastures.  If you have such soybean fields in areas where other fields are maturing, they are worth an extra eye until they reach the R6 (full seed) growth stage.  After R6, the yield is mostly set and insecticide will not provide a return.  Also, if you do spray late in the season, be mindful of the pre-harvest interval of the product you’re using, which can be up to several weeks.  Consult our pest management guide for more information about these chemicals:
https://aginsects.osu.edu/news/msu-osu-insect-ipm-guide

For defoliating insects like grasshoppers, look for defoliation levels across the entire field of around 15% and whether the insects are still present.  A guide to defoliation can be found here:  https://aginsects.osu.edu/sites/aginsects/files/imce/Soybean%20defoliation%20Final.pdf

For stink bugs, which poke directly into the seed with their straw-like mouthparts, take several sweep net samples of 10 sweeps each in different parts of the field.  If you average 4 stink bugs per 10-sweep set (grain) or 2 bugs per set (food-grade and seed) consider treatment.  https://aginsects.osu.edu/sites/aginsects/files/imce/Stink%20bug%20ID%20card%20ID%205_1_19.pdf

Bean leaf beetles pose little threat when feeding on foliage earlier in the season.  Later in the season they may feed directly on the pods, which can cause more damage – either through direct damage to the seed, or through opening the pod to disease.  Inspect all the pods on 10 randomly selected plants and count the total number of pods and the number showing pod injury.  Use your totals to determine percent pod injury.  Treatment is justified if the percent pod injury is reaching 10 to 15%, and bean leaf beetle adults are still present and active.