Outside of finishing planting the crop in soggy areas, monitoring bean leaf beetle populations are one of the first tasks you face this year.

Although early planting is a time-tested method of boosting soybean yields, it does attract bean leaf beetles. This year’s mild Corn Belt winter may mean higher bean leaf beetle populations than in recent years.

One quirk regarding this pest is it can plague soybeans several times during the growing season. That’s due to its three generations per year. The generation that surfaces after planting is the overwintering generation. This generation lays the eggs that hatch in early July, which in turn lays eggs that generally surface around seed fill. Another complicating factor regarding bean leaf beetles is that all three generations spread bean pod mottle virus (BPMV), a yield-reducing disease.

So what do you do? Since bean leaf beetles can do damage quickly, it’s important to scout your fledgling crop. Bean leaf beetles can be controlled through either a pyrethroid, organophosphate, or carbamate insecticide. Treatment hinges upon infestation levels and market price. One guideline you may use for determining early-season treatment of bean leaf beetles developed by Iowa State University entomologists can be found here. This chart pits early-season growth stages against treatment costs and soybean market values in determining threshold levels.

Even if you don’t treat the first generation, early-season scouting can form the basis for second-generation control. If beetle numbers are high enough, second-generation treatment can be justified. You may obtain threshold numbers here.

Soybean insecticide seed treatments like CruiserMaxxPak and Gaucho can also control bean leaf beetles and other early-season insect pests. They work particularly well in fields with a history of early-season insect infestations. However, they can add extra cost if no insect problems surface. “There’s no guarantee there will be an insect outbreak where they can pay off,” says Larry Heatherly, retired research agronomist, USDA-ARS soybean research unit, Stoneville, Mississippi.

Gil Gullickson
Crops Technology Editor, Agriculture.com