For many of you this story may be premature. Due to spotty showers, especially in the southern half of Indiana, your soybean seed is still in the sack. But for others, fields of soybeans are planted and up. One of the early-season pests to watch for is bean leaf beetles.
Note the damage that this pest can do in the picture below. This seed was not treated with any type of seed treatment before planting.
According to the Purdue University Corn & Soybean Field Guide, prepared by the Purdue Diagnostic Training Center, bean leaf beetles typically have two generations per year. Basically, they can attack all season long. The first generation of beetles lays eggs that hatch into the second generation. Damage can continue all the way to harvest. Pod feeding can become severe enough in extreme cases that insecticide application is warranted to protect further damage.
The beetles can be yellow, tan or red. All have a distinctive black, triangular marking behind the head. There may or may not be black spots on the wing covers themselves.
Just because you see damage, especially at this stage, doesn't mean you need to treat. Entomologists recommend sampling an entire field to determine if there is enough activity to warrant treatment. Plants in the vegetative growth phase can handle more leaf loss without impacting yield potential than later when soybeans are in the reproductive phase.
If you're going to scout, inspect five plants in five areas of a field and estimate total percent of leaf loss. It's important to check different areas of a field because the presence or concentration of beetles may not be uniform throughout the field.
The threshold is actually 40% yield loss as long as the soybeans are not blooming or podding. Then the percent defoliation the plants can stand drops dramatically. Consult with your dealer or Extension educator for insecticides that could handle the pest if you have fields over the treatment threshold.