Effects of Glyphosate and Surfactant Concentrations on Giant Burreed (Sparganium eurycarpum) Control with a Ropewick Applicator

Abstract

Field and laboratory experiments were conducted to evaluate the effect of glyphosate concentration, surfactant concentration, and ammonium sulfate on the control of giant burreed when applied through a ropewick applicator. Under non-flooded conditions, a 30% (v/v) solution of glyphosate applied with a ropewick applicator gave the highest giant burreed injury in 1987 and 1988, and reduced corm and rhizome viability compared to the nontreated control in 1987. Warm, dry conditions may have been responsible for poor long-term control in 1988 by reducing translocation of glyphosate to rhizomes. Addition of ammonium sulfate or surfactant did not influence glyphosate toxicity to giant burreed when applied with a ropewick applicator. In the laboratory, leaf necrosis at the point of application was observed with surfactant at 0.6% or 1.2% regardless of glyphosate concentration. Absorption of14C-glyphosate increased two-fold with the addition of surfactant, and translocation to roots and rhizomes decreased almost two-fold as surfactant concentration was increased from 0 to 1.2%. Electrolyte leakage increased with 30% glyphosate when surfactant concentration was increased from 0 to 1.2%. Localized leaf necrosis and disruption of tissues inside the leaf may be responsible for reduced giant burreed control with glyphosate and surfactant applied in high concentrations.