Managing Corn Earworm in Soybeans
Corn earworm/tobacco budworm can defoliate soybeans, 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. This year, I have noticed a bit of an early start to our flight, but only a consistent and moderate trickle of egg lay in the soybeans. With rain, we could see a nice flush of moths emerging from pupation.
Corn earworm (not tobacco budworm) can usually be controlled with pyrethroids- unless there are resistant worms present. Note that we have results from adult vial tests (collected in Washington and Beaufort Counties) performed during this week indicating that 27% of this population could be classified as pyrethroid resistant. Based on what we’ve seen in previous years, fields just at or slightly above threshold could probably be managed with a pyrethroid. Growers with fields under heavy infestations should switch to a worm-specific material.
Resistant earworms and tobacco budworm should be controlled with a worm-specific insecticide (such as Belt, Blackhawk/Tracer, Intrepid Edge, Prevathon or Steward). Earworms and budworms are very difficult to tell apart without specialized training. You can send samples to the NCSU Plant Disease and Insect Clinic for identification. Some county agents have the expertise to do this, as well. If you are not able to identify the insect, you could roll the dice and try a pyrethroid as a first shot. If this fails, you could then switch to one of the worm-specific materials listed above. Alternatively you could play it safe and spray the worm-specific material first.