Estimating Soybean Leaf Defoliation July 26, 2017
Several insects have been observed feeding on soybean leaves recently, including caterpillars, Japanese beetle adults, and grasshoppers. In eastern Nebraska we have received several reports of painted lady caterpillars and silver spotted skipper caterpillars in soybeans. These are sporadic pests of soybean that have distinctive appearances which aid in their identification.
Make treatment decisions for these insects based on levels of defoliation observed. In reproductive soybeans, treatment is recommended if defoliation levels exceed 20% and insects are present. Several of these insects tend to feed in the upper canopy. Be sure to make treatment decisions based on overall defoliation throughout the canopy, not just that seen in the upper canopy. See Figure 2, developed by Justin McMechan, for a recommended sampling procedure to estimate defoliation.
For more information see Managing Soybean Defoliators (NebGuide G2259) .
If insecticide use is warranted, see 2017 Guide for Weed, Disease, and Insect Management in Nebraska (Extension Circular 130) for a list of insecticides labeled in soybeans, rates, restrictions and labelled pests.