Dose–Response of Newly Established Elephantgrass (Pennisetum purpureum) to Postemergence Herbicides

Abstract

Elephantgrass has been proposed as a potential feedstock for biofuel production in south Florida. To limit future invasion of escapes in sugarcane and vegetables, the response of newly established elephantgrass to glyphosate, clethodim, sethoxydim, asulam, and trifloxysulfuron was determined using dose–response curves. Log-logistic models were used to determine the herbicide dose required to produce 90% growth reduction (GR90). The GR90values for shoot biomass at 21 d after treatment (DAT) were 477 g ae ha−1of glyphosate, 262 g ai ha−1of clethodim, 381 g ai ha−1of sethoxydim, 12 kg ai ha−1of asulam, and 94 g ai ha−1of trifloxysulfuron. The GR90values for root biomass at 35 DAT were 570 g ae ha−1of glyphosate, 257 g ai ha−1of clethodim, 432 g ai ha−1of sethoxydim, 17 kg ai ha−1of asulam, and 183 g ai ha−1of trifloxysulfuron. Elephantgrass was predicted to exhibit 97, 98, 75, 1, and 5% mortality after application of glyphosate, clethodim, sethoxydim, asulam, and trifloxysulfuron, respectively, at the label use rates 35 DAT. Results suggest that glyphosate and clethodim will provide control of newly established elephantgrass at label use rates for spot treatments and in vegetables, respectively. Rates higher than the label use rate of sethoxydim will be required to provide acceptable control of newly established elephantgrass in vegetables. However, newly established elephantgrass was not controlled by asulam and trifloxysulfuron at label use rates, implying that control of escapes will be difficult in sugarcane.