Velvetbean caterpillars threaten peanuts, soybeans

Farmers and scouts need to be on-guard for velvetbean caterpillars as they generally strike peanut and soybean fields in the first few weeks of August. They are voracious feeders and can quickly defoliate a peanut or soybean field.

Dimilin 2L received a label for peanuts this year and an application of 2 ounces per acre with the next peanut fungicide application would be good protection against this frequent pest.

This Dimilin application may eliminate insecticide applications growers are applying to control late-season velvetbean caterpillars in peanuts. Also, it may help eliminate a solo insecticide application by combining Dimilin with a routine fungicide spray. Dimilin has excellent residual and normally gives season-long control of velvetbean caterpillars. Dimilin will also help control or suppress other worms including green cloverworms, armyworms (beet, fall, southern and yellow-striped), soybean looper (suppression) and grasshoppers.

University of Georgia research has consistently shown yield increases of 10 percent or more on soybeans with an application of Dimilin 2L at 2 ounces per acre along with boron when pod growth begins (pods are three-sixteenths inch long at the four uppermost nodes of the main stem). This usually occurs in the first weeks of August. This also will be an excellent time to combine a fungicide for Asian soybean rust.

Dimilin is not an insecticide but an insect growth regulator that interferes with chitin deposition (chitin is the protein that serves as the cell wall), and the worms are unable to form an exoskeleton.

After eating Dimilin, worms are unable to successfully molt and go to the next stage. Dimilin is not systemic, so good coverage is critical. Dimilin may not work as well with night fungicide sprays when the leaves are folded, and it will not protect new growth that is put on after the material has been sprayed.

Young velvetbean caterpillars “loop” when they crawl until they are about one-half inch long. They can be distinguished from loopers since they have four pair of prolegs (hind legs) and loopers have only two. They also have a yellow head capsule and will wiggle violently when disturbed or handled.

They are usually green with yellowish-white stripes running down their bodies. Brown or black color phases with yellow stripes may also be found late in the season when populations are high.

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