By Larry Reichenberger

Farmers know they can’t count on a crop until it’s in the bin. But there’s nothing more frustrating than losing a part of it just before the combine gets to the field. That’s what soybean growers in some Midwest and Southern states are experiencing as a result of damage by the soybean stem borer.

This small, long-horned beetle – officially known as the Dectes stem borer – delivers its heartbreaking damage by causing soybeans to lodge late in the growing season.

“It’s not the biggest threat soybean growers face, but it can be very frustrating,” says Kelly Tindall, entomologist at the University of Missouri Delta Research Center. “Last year, we measured losses of nearly 5 bushels per acre in heavily infested fields. And it’s not uncommon for most fields in hot-spot areas to have infestation levels of 95% to 100%.”

Hot-spot areas for the stem borer have been across Texas, Kansas, and into Nebraska, along the Mississippi and Ohio rivers (Missouri, Kentucky, and Tennessee), and the southeastern states along the Atlantic Coast. In Kansas, the soybean stem borer is spreading in central and western areas. A recent statewide survey found infestations in 64 counties – up from only five counties found in a 1985 survey.

Kansas State University entomologist Phil Sloderbeck explains that stem borer larvae tunnel up and down the inside of soybean stems and end up at the base when plants are mature. “This leaves stems weak and brittle at harvesttime. They break off right at the ground level and often fall flat, making them difficult, or impossible, to recover,” he says.

“Typically, any yield loss to stem borer damage becomes most significant when harvest is delayed. In those cases, we’ve seen 40% to 50% of plants lying on the ground. Depending on the equipment a farmer is using, much of this can be lost. Or, at least, the pace of harvest will be further slowed,” says Sloderbeck.

Sloderbeck says there is no approved method to manage the soybean stem borer. Insecticide options either aren’t available or aren’t practical, and there are no resistant soybean varieties.

“Timely harvesting is one of the few ways to reduce yield loss to soybean stem borer,” he says. “Crop rotation may help, but it’s also not practical if soybean acreage in the area is increasing.”