Midseason Soybean Insects

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Because we won’t be dealing with many kudzu bugs this season (see this article), we need to focus our efforts on the other pests that are around. These include the corn earworm/tobacco budworm, stink bugs and defoliators (loopers, armyworms, etc.).

The first pest we will likely have to manage is corn earworm/tobacco budworm. These insects can defoliate, but are more serious pests of seeds forming in the pod. They should never be sprayed at flowering, but should be controlled when pods are present (especially at R4 to R7). Thresholds vary with sampling method and row spacing; I suggest using the earworm/budworm online threshold calculator as a guide for treatment. Corn earworm can usually be controlled with pyrethroids- unless there are resistant worms present. Resistant earworms and tobacco budworm should be controlled with a worm-specific insecticide (such as Belt, Blackhawk, Prevathon or Steward). Earworms and budworms are very difficult to tell apart without specialized training. I recommend a pyrethroid as a first shot. If this fails, switch to one of the worm-specific materials listed above.

Stink bugs move in an out of soybeans throughout the season. You might notice a lot of them when soybean is flowering (R1-R2), but they do not cause yield loss at this point. Focus your control when the seed is forming (R5-R6). Seed producers should also treat at R7 to avoid quality loss. Like corn earworm/tobacco budworm, the thresholds vary with sampling method and row spacing. You can use the stink bug online threshold calculator to figure out when to treat. Green stink bug can be managed with a pyrethroid. Add in something like acephate (Orthene) or use acephate alone to kill browns.

Image from Iowa State University Extension.

Image from Iowa State University Extension.

Defoliators like soybean loopers and armyworms are more of a problem later on in the season. There are two reasons for this. One is that many are migratory pests that don’t overwinter here. So they can build as the season progresses. The second is that we often treat with a pyrethroid midseason. This is to manage things like earworms and stink bugs and is often needed. The disadvantage is that we knock out all the beneficial good-guy insects, releasing these worms to eat foliage. You should only treat for defoliators when the canopy loss is 15% after bloom. For soybean looper, beet armyworm, and corn-strain fall armyworm, use a worm-specific insecticide (such as Belt, Blackhawk, Prevathon or Steward).