The most effective way to make treatments decisions for pests with chewing mouthparts (e.g., Japanese beetle, bean leaf beetle, caterpillars, and grasshoppers) is to estimate defoliation. I’m a “lumper” and don’t try too hard to distinguish feeding by species. Replicated data over multiple growing regions consistently shows economic thresholds for soybean are 30% in the vegetative stages and 20% in the reproductive stages. This threshold applies to the entire field. Sometimes these pest cause significant injury along field margins and perimeter treatments may be more cost effective if practical.
In a recent ICM News article, I provide a scouting guideline (Figure 1) to help make accurate defoliation estimates. In general, humans tend to over-estimate defoliation and treat more often than necessary. Practice estimating defoliation with Figure 2. I also recently published a review article for Japanese beetle if you want to learn more about this corn and soybean pest.
Erin Hodgson Professor
Dr. Erin Hodgson started working in the Department of Entomology, now the Department of Plant Pathology, Entomology, and Microbiology, at Iowa State University in 2009. She is a professor with extension and research responsibilities in corn and soybeans. She has a general background in integrated...