Black grass bug damage to intermediate wheatgrass forage quality

1. Conclusions: • Black grass bug feeding damage resulted in: • Reduced crude protein • Increased ADF and NDF • Black grass bug damage significantly reduces forage quality Labops hesperius Irbisia elongata Labops hesperius (brachypterous) Black grass bug damage to intermediate wheatgrass forage quality Sue L. Blodgett, Andrew W. Lenssen1, S. Dennis Cash Department of Animal and Range Science, Montana State University, Bozeman, Montana USA 59717 1USDA,ARS, Northern Plains Agricultural Research Laboratory, Sidney, Montana USA 59270 Results: The maximum black grass bug damage recorded (rating = 5) resulted in a 42.4% reduction in crude protein compared with undamaged tissue (Fig 1A). Acid detergent fiber (ADF) and neutral detergent fiber were directly related to black grass bug damage (Fig 1B and 2A). Percent forage sulfur and phosphorus concentrations were inversely related to black grass bug damage ratings (Fig 2B). There was no significant relationship between black grass bug damage and IVDDM. Discussion: Black grass bug damage ratings correlated with intermediate wheatgrass forage quality characteristics. There was a significant decrease in percent crude protein and increases in both ADF and NDF as black grass bug damage increased, indicating that black grass bug had an important impact on forage quality. Todd and Kamm (1974) noted similar reductions in forage quality, although adequate precipitation can mitigate damage. Impact of black grass bug feeding on rangeland productivity varied with rainfall and time of forage utilization, suggesting that greater losses may be expected in drought years. Background: The black grass bug (Labops spp.) Hemiptera: Miridae, (BGB) is native to the western United States and has been reported damaging wheatgrasses coincident with the increase in seeded acreages of wheatgrasses in the western U.S. Black grass bug (BGB) feeding damage has been documented to reduce yield, plant height and seedhead production. Our study was conducted during a drought that had begun in the late 1990s and persisted through this study, conditions that increase the impact of black grass bug feeding (Todd and Kamm 1974). We report significant increases in concentrations of acid and neutral detergent fiber with increasing black grass bug damage, indicative of reduced forage digestibility and ruminant intake, consistent with the rancher’s observations of forage yield reduction and reduced intake by grazing cattle. Malecheck et al. (1977) stated that stockmen have observed that black grass bug infestations decrease forage palatability although they did not detect a significant depression in intake. We found no significant relationship between black grass bug damage and digestibility (IVDDM), in agreement with the sheep digestion-balance trial conducted by Malechek et al. (1977) in which differences in daily dry-matter digestibility and dry matter consumption (intake) were not significant. Objective: Determine the relationship between black grass bug damage and forage quality. Materials and Methods: Five pastures, located near Townsend, MT, were predominantly intermediate wheatgrass with a few alfalfa plants (<1 m2). Since bugs were primarily adults stage and had done substantial damage, BGB damage was rated and leaf samples collected on July 6, 2002 for forage quality analysis. BGB feeding damage, called stippling, is caused when plant cells are pierced and contents are removed. BGB damage was rated on a scale of 0 to 5, (0 = no damage, 1=10-20%, 2=30-40%, 3=50-60%, 4=70-80% and 5=80-100% of the leaf stippled). Leaf samples of each BGB damage category were held separately, dried at 55 oC for 72 hours and then ground to pass a 0.5mm mesh sieve. Percent crude protein, acid detergent fiber (ADF), neutral detergent fiber (NDF), in vitro digestible dry matter (IVDDM), percent sulfur and percent phosphorus were determined using a NIRS System 4500 equipped with InfraTech 2 software. Regression analysis was used to determine relationships between black grass bug damage rating and forage quality parameters. Acknowledgements: Authors wish to thank Mr. Nelson Wert who brought this situation to our attention and allowed us to collect samples from his ranch. References: Todd JG, Kamm JA. 1974. Biology and impact of a grass bug Labops hesperius Uhler in Oregon rangeland. J. Range Manage. 27: 453-458. Malechek JC, Gray AM, Haws BA. 1977. Yield and nutritional quality of intermediate wheatgrass infested by black grass bugs at low population densities. J. Range Manage. 30:128-131.