Hay growers and horse owners beware. High numbers of striped blister beetles are showing up in alfalfa in some areas of Missouri, warns University of Missouri (MU) Extension entomologist Wayne Bailey.

The beetles produce a toxin that can stay in alfalfa hay for at least four to five years after it’s been harvested. If horses consume the toxic hay, they can get sick or even die. The greatest risk for contamination is in second- and third-cutting alfalfa, he says.

Because striped blister beetles move quickly among fields, growers should scout alfalfa frequently to determine pest numbers. If thresholds are high enough, insecticides should be applied, Bailey says.

Not all fields, even on the same farm, will have the beetles, says Rob Kallenbach, MU Extension forage specialist. He suggests quietly walking through fields the day before harvesting and applying insecticide if needed. Noise causes the beetles to drop to the ground to hide, he adds.

He and MU colleague Craig Roberts also suggest cutting late-season alfalfa when 10% or less of alfalfa is in bloom and keeping alfalfa free of weeds.

Avoid the use of crimpers and conditioners, which crush hay and promote drying, Roberts says. And avoid running tires on windrows.