Growers or their agronomists should start scouting fields beginning with emergence and assessing plant stands and early weed emergence and identification in May. In doing this inspection, we may see the first signs of insects and diseases.

By June 20, most soybeans are at R1 – early bloom, even though they will continue vegetative development. Some of the early season’s diseases and insect pests to look for include Septoria brown spot, Japanese beetle and bean leaf beetle.

Bean Leaf Beetle: Bean leaf beetles are an early and late season pest. Early planted soybeans—especially the first fields to emerge in an area—may show signs of seedling injury due to feeding by overwintering adult beetles. Foliar damage appears in late June and continues until fall as a succession of first and second generation adults emerge and feed. If cotyledons are destroyed before unifoliate leaves emerge or the growing point is damaged, reduced yields are likely. 

Once trifoliate leaves have unrolled, soybeans can tolerate up to about 40 percent defoliation from bean leaf beetle feeding without yield loss.

Eric Ifft, Customer Business adviser with Bayer CropScience provided this content on Septoria and Japanese beetles:

Septoria Brown Spot:“Most of us were taught that Septoria Brown Spot is a “minor” disease and therefore does not cause much yield loss in soybeans. While this may have been true when the research was done back in the 1970s, I am not sure it is true today. Practical applications of fungicide on this disease have been showing a significant yield response the last 10 years or so. Reports of this disease showing up early in soybean fields has me slightly concerned. While we know that the biggest reason to treat soybeans with a fungicide like Stratego® YLD is to relieve stress so the soybean plant doesn’t abort as many flowers, treating this fungal disease could be an added benefit.”

Small, angular, light brown lesions form on leaves, later becoming brick red to chocolate brown. Lesions appear early in the season but are found only in the lower canopy until plants approach maturity. Severally affected leaves may drop prematurely.

Japanese Beetles: “It has been a few years since we have had to deal with Japanese beetles, but I wanted you to know that there are reports of Japanese beetles being found in central Illinois. Below is a picture I took a couple of years ago of Japanese beetles doing damage to soybeans in Peoria County. If we have an infestation, an insecticide like Leverage^® 360 is great for knockdown and in plant residual protection from this important pest.”

Agronomist Dr. Daniel Davidson posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com or ring him at 402-649-5919.