How Late Should I Treat Insects in Soybeans?

— Written By

Most of our field crops are transitioning into insect safe stages, except for soybeans. At this point in the season we are primarily worried about protecting double cropped beans. However, as the late great Yogi Berra quipped, “it ain’t over till it’s over”. Pests to watch out for include those in the defoliating complex and stink bugs. This generation of earworms usually doesn’t establish well, trap catches are trending down in most locations, and they prefer to lay eggs in blooming soybeans, of which we have very few. So we should be out of the woods with them.

Defoliating complex: common problem insects include armyworms, bean leaf beetle, and soybean looper. Armyworms and loopers tend to be more of an issue in coastal counties. Soybeans should be protected until R7 (the point at which a single pod on a plant has turned mature color); our threshold is 15% defoliation of the entire canopy after bloom. A good guide to estimating defoliation can be found here.

Stink bugs: stink bugs can begin to injure soybeans once pods are present (R3) through R6 (full seed). They can still damage soybeans through R7, but less so than during the previous stages. For this reason, some folks choose to relax the threshold at this stage. Seed producers should be more conservative to preserve germination quality. Thresholds can be found here. Stink bugs tend to pile into soybeans later season as other crop hosts are harvested in the system and now is also the time when reproduction is happening. After the fall equinox (late September), the adults that have developed from this generation will slowly disperse to overwintering habitats.