As distributors begin to stock up insecticide inventory for the season, it is a good time to lay out a management strategy for corn earworm control in soybeans. 

This has been our most consistent soybean insect pest, sprayed on the majority of our acres in most years. I am predicting this year’s pressure will be similar to last year, which is to say relatively light.

Below are my suggestions going forward:

•  Although soybeans should be scouted throughout the season (think kudzu bug), begin scouting for corn earworms on soybeans that are flowering. These are very attractive places for moths to lay eggs. Scout at several places in the field, using a drop cloth rows above 30 inches and a sweep net for narrow row or drilled soybeans.

• There are very few cases where corn earworms impact flowering soybeans. Recent research was conducted by a student working under me, Rachel Suits. This work, supported by the North Carolina Soybean Producers Association, proved that flowering soybeans can tolerate at least 2-3x the corn earworm threshold levels of podding soybeans. In fact, we were not able to create a situation in the field where corn earworm could cause a yield loss in flowering soybeans. Therefore, the threshold for flowering soybeans is likely much much higher than in podding soybeans.

I have heard that some folks would like to eliminate corn earworm while plants flower to protect pods from larger worms that developed in the flowering stages. This is not a good idea since the worms tend to be very small (first and second instar) during flowering and will hide in the blooms, making control difficult. 

Also, sprays impact natural enemies that can come in and reduce developing populations of corn earworm. The worst infestations of corn earworm, beet armyworm, and loopers that I saw last year were in fields where pyrethroids were sprayed automatically at flowering.

Scout during flowering to see how populations are developing. You can then be ready to spray during podding stages (R4 and greater), when soybeans are susceptible to yield loss.