Utah Pests News Summer 2009

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Black Grass Bug Explosion in Utah Rangelands

The UPPDL has received numerous reports of black grass bug outbreaks this spring. Thousands of acres have been affected in Sevier, Juab, San Juan, Cache, and Box Elder counties. Farmers and ranchers in areas of higher elevation with cooler temperatures should be on the lookout for grass bugs.

Black grass bugs, which are actually a complex of related insects, are not new to Utah. Favorable conditions in recent years have helped increase their populations to damaging levels in rangeland, forage, and field crops. In particular, blue bunch wheatgrass, crested wheatgrass, and intermediate wheatgrass are grass bug favorites, but wheat, barley, oats, and rye may also be affected. Once black grass bug nymphs are detected in the spring, control is limited to insecticidal sprays containing acephate, carbaryl, lambda-cyhalothrin, malathion, and methyl parathion.

Black grass bugs overwinter as eggs, and have one generation per year. Egg hatch begins in the spring and adults will remain active for 5 to 6 weeks, sucking the chlorophyll out of host plants. They then lay eggs within grass stems.

The large populations of grass bugs this year will likely yield a large population for next year, so farmers and ranchers should think about next year’s control now. The key to suppression is to burn or graze the field in summer to diminish overwintering eggs, and reduce the need for insecticides next year.

-Ryan Davis, Arthropod Diagnostician

Click here for USU black grass bug fact sheet.