Technical Abstract: Black grass bug (Labops hesperius Uhler.) also known as the wheatgrass bug and grass bug, is an important pest of wheatgrass species. Infestations can decrease yield and persistence of wheatgrasses. A rancher near Townsend, MT, USA, observed yellowed foliage and poor productivity of five intermediate wheatgrass (Thinoyron intermedium (Host) Barkworth & D.R. Dewey) pastures. Feed intake was poor and cattle were losing weight and condition. One hundred leaf blades were randomly selected from each pasture and rated for black grass bug damage based on stippling using a scale of 0 to 5 (0 = no damage and 5 = > 80% of the leaf stippled). Increasing black grass bug damage of intermediate wheatgrass resulted in decreased crude protein and increased neutral and acid detergent fiber concentrations of leaf blades. Producers should monitor intermediate wheatgrass pastures for black grass bug infestations, and when populations are high, use cultural and/or chemical control measures to protect potential forage yield and quality, and grass persistence.