Black grass bugs (Hemiptera: Miridae) have been causing problems in Conservation Reserve Program land and pastures in Adams and Bowman counties in southwestern North Dakota.

The heavy infestations in some cases have caused the black grass bugs to move into adjacent wheat and barley fields.

“Black grass bugs feed on a variety of grasses, such as crested wheat grass, brome grass, bluegrass and orchard grass, and field crops, such as wheat, barley, rye and oats,” says Jan Knodel, North Dakota State University Extension Service entomologist. “Crested wheat grass is the most preferred grass. Adult and nymphs feed by piercing and extracting the green (chlorophyll) tissue from the plants. This causes white spots and blotches to form on plant foliage. Heavily infested plants can appear frosted. Small black spots of excrement covering the plants also are symptoms of heavy feeding activity.”

Heavy feeding damage can reduce yield, plant height and seed head production, especially during dry years. Plants can recover if the moisture is adequate for plant growth. Black grass bugs also can affect forage grass quality by reducing crude protein and increasing acid detergent fiber. Therefore, cattle eat less black grass bug damaged forage and the feed quality is poor.

Black grass bugs prefer monoculture grasses, so planting a polyculture can reduce feeding damage.

Insecticide control typically is not recommended for CRP land, rangeland or pastures unless the grass is being grown for seed production. No economic threshold has been developed for black grass bugs. However, populations that exceed 1,000 bugs per square foot can kill a plant.

“One well-timed insecticide application targeting the nymphs and adult females prior to laying egg easily can control black grass bug populations,” Knodel says. “Some active-ingredient insecticides registered in North Dakota for black grass bug control in rangeland grasses used for grazing or haying are carbaryl (Sevin), malathion and zeta-cypermethrin (Mustang Max). Some active-ingredient insecticides registered in noncrop areas (not for grazing or haying) in North Dakota are acephate (Orthene) and lambda-cyhalothrin (Warrior or Lambda - Cy EC).”

Insecticides will kill the adults and nymphs but not the eggs in the stems. Knodel adds that producers need to remember that black grass bug control with insecticides typically is not practical or economical in rangeland or pasture. Mowing, haying and grazing in late fall or early spring is recommended to reduce the number of egg-laying sites and eggs.

“Black grass bugs will move into small-grain crops, such as wheat, that are adjacent to infested grassy areas,” Knodel says. Typically, only the field edges of the wheat are infested. Wheat can sustain quite a bit of black grass bug feeding injury without significant yield losses unless the flag leaf is severely damaged or the wheat is stressed by moisture, fertility or other pests.”

Lambda-cyhalothrin (Warrior II) will control black grass bugs in wheat and barley and zeta-cypermethrin (Mustang Max) will control black grass bugs in wheat only.

NDSU Agriculture Communication