Perennial weed control with glyphosate

Field experiments were conducted to evaluate in-season use of glyphosate for perennial weed control. Examination of cotton yield, johnsongrass stem and plant count reductions, illustrates that glyphosate provides adequate johnsongrass control. Although control was less than that achieved with clethodim applications, it was acceptable, especially if its activity on other weedy species is also considered. When glyphosate was tank mixed with fluometuron it resulted in less johnsongrass control than with glyphosate alone; however, when MSMA was tank mixed with glyphosate, efficacy increased. When a three way mixture of glyphosate + MSMA + fluometuron was evaluated no antagonism was observed thus indicating MSMA helped overcome the negative effects of fluometuron. The addition of pyrithiobac had little effect on johnsongrass control with glyphosate. Johnsongrass control with fall applications of glyphosate applied as a tank-mix with cotton defoliants resulted in control equivalent to that achieved with glyphosate alone.