Kudzu bug populations are all over the place right now in terms of how they are developing. Believe it or not, this second generation was not as bad as I had predicted (the first generation was worse). However, we are still consistently spraying fields for this insect. Here are a couple pointers for management going forward.
Soybeans are “kudzu-bug safe” once they reach R7 (one mature-colored pod on the plant). This goes also for our defoliating pests that don’t attack the pods or seeds (such as loopers and bean leaf beetle).
Kudzu bug population development is very erratic on a field-to-field basis. Some soybean fields have already finished up their second generation of kudzu bugs and some are finishing up now. There are only two generations of kudzu bug a year so if you see adults now, rest assured that they won’t lay eggs. Adults that we see now are going to form our overwintering generation. We’ll see these again next May and June in our early-planted beans.
If you’ve sprayed for kudzu bugs and are noticing adults moving back into the field, this is normal. We get very little, if any residual from any insecticide with this insect. Adults can feed and cause injury and I’m we don’t have great information on what sort of damage these adults can cause. My gut feeling is that these adults are hanging around in soybeans until they receive the cue to migrate to overwintering sites. We’ll see this happen soon as the days become shorter. Spraying these adults now is probably not economically justifiable unless populations are really heavy or beans are not near R7. Most of our early beans that are attractive to kudzu bug are mature or close to maturity.
Finally, you might see kudzu bug adults move into double-cropped beans in October like we did last year. These adults moved into fully mature defoliated beans for one last hurrah before overwintering in their favorite spots (behind loose tree bark and underneath leaf litter). I don’t think we’ll need to worry about these migrating bugs passing through, especially since beans should be mature by then.