Georgia peanut growers need to check their fields this week for velvetbean caterpillar (VBC) infestations. Moths have been present for several weeks, and populations of caterpillars are now at threshold in many fields. A field of mine that has not been treated with insecticide was averaging 20 caterpillars per row foot on Monday afternoon (31 Aug); most of the caterpillars were VBC. This pest is generally easy to kill, but it has a huge appetite and can completely defoliate peanut fields if left untreated. Peanut can tolerate some defoliation with no loss of yield, but we do not want to see fields stripped of leaves when they still have several weeks left to mature the crop.
How to sample: Check several location within each field (10 is a good number). Most folks are going to quit sampling before they get to 10 if caterpillar numbers are high, but it is still a good idea to cover the whole field. Sample three feet of row at each stop. Remember the threshold is based on caterpillars per row foot not per three row feet. Count the number of worms in the three foot sample and divide by three. Don’t get in a huge hurry. Once you vigorously beat the foliage, take your time to count the caterpillars. The big ones will be obvious, but it will take a little time for the tiny ones to start moving around…they are nearly impossible to see/count when they are still. Be sure to identify the caterpillars you see. Misidentification can be very costly if the wrong insecticide is used.
The threshold for caterpillars is 4 to 8 per row foot depending on the condition of the vines (healthy, vigorous vines can tolerate more feeding that stressed or stunted vines). If you have questions about caterpillars or other insect management issues in peanut, contact your local UGA county Extension agent.