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Things to Consider about Brown Marmorated Stink Bugs and Your Senescing Soybeans

Posted: September 9, 2011

By John Tooker, PSU Entomology Specialist

Field Crop News, Vol. 11:25, September 6, 2011

Brown marmorated stink bug populations are certainly distributed unequally across Pennsylvania. We continue to hear of fields with large populations of bugs in southern Lancaster County, but we have also heard of folks looking for stink bugs in Franklin, Berks, Lehigh, and Schuylkill County who have not found many at all. I would continue to keep an eye out for the bugs, particularly in the southern counties (southern portions of south counties) because their populations can build quickly. Soybeans will, however, begin to senesce soon, and that will decrease, but not eliminate, the risk posed by stink bugs, which brings me to an issue I want to address.

Stink bugs begin leaving fields and seeking places to overwinter in mid-to-late September. We know this because around 20 Sept the past few years, the number of hits on the brown marmorated stink bug fact sheet (http://ento.psu.edu/extension/factsheets/brown-marmorated-stink-bug) on the Dept. of Entomology factsheet really increases. We credit this activity to homeowners seeking information about this pest when they begin encountering it in their homes.

Despite starting to leave fields in late September, stink bugs remain a concern for soybean yield right up to harvest. Stink bugs feed on soybeans through the wall of the pod and extract moisture. When they feed they inject saliva, which begins extra-oral digestion, and then they suck up the predigested plant tissue. So it seems that stinkbugs should be able to feed on drying soybeans as long as they are found in fields, meaning that growers might need to protect their beans for weeks to come. Growers will have to balance the population size of stink bugs, the cost of a treatment, and the cost of running down of the crop to make the application.

Stink bug feeding can also cause a condition often referred to as “stay green.” This occurs when plants that have been feed upon stay green longer, apparently in an attempt to compensate for the feeding damage they received. This stay green syndrome can be problematic because different parts of the field may senesce at different rates and the entire field will not be ready for harvest at the same time. Growers in Virginia and Maryland have noticed ‘stay green’ on the edges of field where stink bug populations were highest.

All this information leads to the simple conclusion that growers with stink bugs populations in their fields have decisions to make. Each grower is going to have to assess their own situation, balancing bug population size, stage of the beans, harvest date, etc., but it is safe to say that if stink bugs are present in populations exceeding the economic threshold we are using (2.5 stink bugs per 15 sweeps in narrow-row beans and 3.5 stinkbugs per 15 sweeps in wide-row beans), they could be causing yield loss that may need to be addressed. See the Pest Management portion of Penn State’s Agronomy Guide for some treatment options (http://extension.psu.edu/agronomy-guide/pm)