Soybean loopers are the dominant caterpillar species occurring over a multi state area of the southeastern United States. Several states, including Arkansas, Georgia and the Carolinas are all experiencing looper outbreaks. I observed my first soybean field with treatable levels of loopers in Baldwin county on 8/26. Based on what is happening over a large area, Alabama growers need to be very alert for looper outbreaks.
Soybean loopers may occur at damaging levels in soybeans, peanuts, or late maturing cotton fields. Looper eggs are deposited on the underside of leaves in the lower part of the crop canopy. The tiny, hair like, early instar larvae can go undetected for several days. As they mature they move up the plant canopy with their defoliation. Therefore, the foliage loss is often unnoticeable for a week or more. A high percent of the total foliage consumed is during the last 3-4 days of the larval cycle. I have always considered somewhere between 5 and 8 larvae per row foot as an economic level. The amount of canopy available in a crop like soybeans would have some bearing on the economic threshold. I will have to depend on my entomology friends to set a sweep net threshold for drill soybeans. I’ll be checking around for that threshold since late planted drill beans behind wheat may be at the greatest risk.
Insecticides that work well on soybean looper are: Steward, Intrepid, Tracer, and recently labeled Belt. Both Diamond and Dimilin (Insect Growth Regulators) also give adequate to good suppression. Products like pyrethroids, Lannate, Larvin, Sevin, Lorsban and methyl parathion do not give measurable control of soybean loopers in Alabama.