There have been several reports of fall armyworms in wheat beans. Fields with weedy grasses or volunteer wheat are especially prone to infestations. The larvae start out on grasses and move to soybean (usually after a herbicide application takes the grass out). However, fall armyworms can sometimes make an appearance even if the fields are not grassy.

The treatment threshold for armyworms or other defoliators in pre-flowering soybean is when 30-35% defoliation has occurred. But you may consider treatment if large numbers are being observed on grasses in the fields or when 40 or more are found per 100 sweeps. Make sure you look closely on the grass of any grassy fields if you start seeing fall armyworms in your sweep net. Generally, we are dealing with the “Bermudagrass strain” of armyworms in soybeans, and pyrethroid insecticides will provide good control.