Alison M. Fox, Doria R. Gordon and Randall K. Stocker
Tyler J. Koschnick, William T. Haller and Alison M. Fox
Two formulations of the contact herbicide endothall are used to control submersed aquatic weeds. Waters treated with the amine or dipotassium salt formulations have irrigation restrictions varying from 7 to 25 days depending on the concentration of endothall applied. These water-use restrictions may be reduced for turfgrass if studies conclude there is no phytotoxicity to turf species irrigated with concentrations of endothall that may exist after an aquatic application. Two separate experiments were conducted to determine turfgrass tolerance to endothall in irrigation water on five species of grass: annual ryegrass (Lolium multiflorum), annual bluegrass (Poa annua), centipedegrass (Eremochloa ophiuroides), `Floratam' st. augustinegrass (Stenotaphrum secundatum), and `Tifton 419' bermudagrass (Cynodon dactylon). Expt. 1 used constant concentrations of endothall; Expt. 2 used decreasing concentrations of endothall over time. Annual turf species (bluegrass and ryegrass) were generally more susceptible than perennial turfgrasses. Concentrations resulting in a 10% reduction in total dry weight harvested compared to control plants [effective concentration (EC10)] for the amine and dipotassium salt formulations were 10 and 14 mg·L–1 (ppm) a.i. on annual ryegrass, 10 and 16 mg·L–1 a.i. on annual bluegrass, 50 and 54 mg·L–1 a.i. on centipedegrass, 47 and 72 mg·L–1 a.i. for st. augustinegrass, and for bermudagrass 1301 and 908 mg·L–1 a.i. in Expt. 1. Expt. 2 resulted in EC10 values of 31 and 35 mg·L–1 a.i. on annual ryegrass, 7 and 12 mg·L–1 a.i. on annual bluegrass, 32 and 99 mg·L–1 a.i. on centipedegrass, 27 and 20 mg·L–1 a.i. on st. augustinegrass for the amine and dipotassium formulations of endothall respectively, and 958 mg·L–1 a.i. for the dipotassium formulation on bermudagrass. There was no effect on bermudagrass dry weights when exposed to the amine formulation of endothall in Expt. 2 at concentrations up to 1600 mg·L–1 a.i. There is a low risk of inhibiting growth of turf species at endothall concentrations used for aquatic weed control considering the maximum use concentrations, typical uses of the products, and decomposition rates.