Activity of Glyphosate on Johnsongrass

Abstract

Glyphosate [(N-phosphonomethyl) glycine] was evaluated for three years as a foliar herbicide for the control of johnsongrass [Sorghum halepense (L.) Pers.]. In the greenhouse, maximum rhizome kill resulted from foliar applications of glyphosate at 1.12 to 2.24 kg/ha. In several field studies, plowing from 4 to 21 days following glyphosate application had little effect on johnsongrass control; plowing within 0.5 hr following glyphosate application resulted in less control than when plowing was delayed for 12 days. In stage of growth studies, control was better when glyphosate was applied to johnsongrass in the boot to full head stage than earlier when johnsongrass was 45 to 60 cm in height. In ‘York’ soybeans [Glycine max (L.) Merr.], glyphosate at 1.12 to 2.24 kg/ha applied 12 to 14 days prior to plowing and trifluralin (a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) incorporated prior to planting provided good johnsongrass control. In ‘3369A’ corn (Zea mays L.) directed postemergence applications of glyphosate provided good johnsongrass control but caused extensive crop injury.