Hessian fly on wheat. Photo courtesy of Scott Bauer. Licensed under
CC BY 3.0
Hessian flies are a tiny pest of wheat, barley, and rye. Historically it was a significant pest but the cultural practice of planting wheat later in the fall has reduced their impact.
Adult Hessian flies are about 1/8" in length. They are grey or black in color.
Larvae are pale yellow in color and are legless. They lack a defined head.
Adults lay eggs in the spring, with the resulting larvae feeding on the stem. The stem is weakened and typically breaks before harvest.
Hessian flies cease to be active in the late fall. Planting after this "fly-free" date reduces the likelihood that a field will be infested with damaging larvae the following spring.