Johnsongrass (Sorghum halepense) Control by Herbicides in Oil Diluents

Abstract

Control of seedling and rhizome johnsongrass [Sorghum halepense(L.) Pers. # SORHA] with five herbicides was evaluated after postemergence application in various diluents and spray volumes using one to three types of applicators from 1983 to 1985. The rate of each herbicide required to control seedling johnsongrass using paraffinic oil as the diluent in applications with an external- or internal-mixing air-assist sprayer at a spray volume of 9.4 L/ha was one-half the rate required when water plus 1.25% (v/v) paraffinic oil concentrate (POC) or water plus 1.25% (v/v) soybean oil concentrate (SOC) were the diluents in applications with a conventional sprayer equipped with fan jet spray nozzles at a spray volume of 187 L/ha. Rates were also reduced when once-refined soybean oil was the diluent at a spray volume of 9.4 L/ha, except for the ethyl ester of quizalofop {(±)-2-[4-[(6-chloro-2-quinoxalinyl)oxy] phenoxy] propanoic acid}. Sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} was equally effective on seedling johnsongrass growing in soybeans [Glycine max(L.) Merr. ‘DPL 105’] when applied at 224 g ai/ha with an internal-mixing air-assist sprayer or a controlled-droplet applicator (CDA) at a spray volume of 9.4 L/ha and a conventional sprayer at a spray volume of 187 L/ha, regardless of diluent. Conventional application required the use of 1.25% (v/v) SOC or POC as part of the diluent to be effective. For three of the five herbicides evaluated on rhizome johnsongrass, paraffinic oil at a spray volume of 9.4 L/ha was the only diluent that resulted in season-long control. Rhizome johnsongrass control with this diluent also resulted in significantly higher soybean yields than all other diluent-spray volume treatments.