Forage Quality Responses of Selected Grasses to Tebuthiuron

Abstract

Tebuthiuron pellets (20% active ingredient [a.i.]) applied at 0.6, 1.1 or 2.2 kg/ha (a.i.) to native stands of little bluestem and at 1.1 or 2.2 kg/ha to l-year-old seeded stands of Bahiagrass, Bell rhodesgrass, green sprangletop, and little bluestem did not significantly alter the in vitro digestible organic matter concentrations of grass leaves. Leaf water concentrations of Bahiagrass, green sprangletop, and little bluestem were not consistently altered by application of tebuthiuron. However, application of 1.1 or 2.2 kg/ha of tebuthiuron pellets to seeded stands or to native little bluestem increased foliar crude protein concentrations. Application of 0.125,0.188, or 0.25 ppm of tebuthiuron in aqueous solutions to pots containing grasses in the greenhouse significantly increased foliar crude protein concentrations, compared to that of untreated plants. Crude protein concentrations were increased only during the growing season of application in the native stand of little bluestem. These results suggest application of tebuthiuron for brush control may enhance rangeland forage crude protein concentrations while not affecting in vitro digestible organic matter. Research on herbicides for brush management traditionally has emphasized efficacy as related to dosage and time of application with lesser emphasis on forage responses. Most studies of range forage responses to herbicide application have evaluated changes in standing crop and botanical composition of herbaceous stands as attributed to selective removal or suppression of associated woody species. However, sublethal applications of some herbicides may significantly alter various physiological processes within some forage species (Reis 1976). Nutritional constituents, such as crude protein, have increased following applications of simazine [2chloro-4,y-bis(ethylamino)-s-triazine] (Allinson and Peters 1970) or atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-~-triazine] (Raker et al. 1980). The physiological mode of action of tebuthiuron [N-(5-(1 ,Idime