Black grass bugs are damaging crested wheatgrass and intermediate wheatgrass in western South Dakota, and some have moved into wheatfields in some locations.

Sandy Huber, SDSU Extension's agronomy educator for Bennett County, said she's seeing infestations of 165 insects or more in ten sweeps of a net.

"I am seeing and hearing problems with Black grass bugs in Bennett, Shannon, Haakon, and Jackson Counties," Huber said. "The populations seem to have been building during the drought years and some producers have had two or three years where the damage was so severe that hay fields were not hayed. Since the bugs make the grass unpalatable to livestock, there is reduced intake."

The insects cause wheatgrass in pastures and hayfields to turn a yellowish color instead of green. Infestations result in a stippling on leaves that causes the forage to lose quality, Huber said.

Perkins County Extension Educator Bob Drown said the insects are also causing significant damage in parts of Meade and Harding counties. Though some wheatfields are experiencing damage — enough for a few West River producers to spray — Drown said black grass bugs prefer to feed on wheatgrass. Huber and Drown said some producers are already spraying hayfields.

With grass hay ranging in price from $90 to $110 a ton, Drown said, some producers are penciling out treatment costs and deciding to spray.

"When coupled with drought, these insects can make the difference between having any hay to make or not, or having enough pasture," Drown said.

Fall River County Extension Educator Mark Fanning and Butte County Extension Educator T.J. Swan are also reporting considerable damage from the pests in some locations in Fall River and Meade counties.

SDSU Extension Entomologist Mike Catangui said black grass bugs are native insects, but their increase in numbers appears to be correlated with widespread plantings of imported wheatgrasses such as crested wheatgrass and intermediate wheatgrass. Black grass bugs are about one quarter of an inch long and have syringe-like mouthparts that they use to pierce grass leaves with and withdraw sap from.

They overwinter as eggs in grass stems then hatch in the spring as grasses begin to re-grow. It takes about a month for them to transform from eggs to adult black grass bugs. There is one generation a year and numbers usually decline by the end of June once they are finished laying eggs.

No formalized economic thresholds are currently available for black grass bugs on grasses, Catangui said. Sevin XLR (0.5-1.0 pint per acre) is labeled for use against black grass bugs on perennial grasses in South Dakota. Always read and follow label directions.

Source: SDSU AgBio Communications