Turf and Ornamental Plant Tolerances to Endothall in Irrigation Water I. Ornamental Species

Abstract

Restrictions on the endothall aquatic herbicide label include the use of endothall treated water for irrigating plants from 7 to 25 days after application. This interval was established to allow sufficient time for endothall to dissipate to levels that were considered safe for irrigation to prevent phytotoxicity to desirable plants. The affects of endothall on begonias (Begonia semperflorens `Vodka Cocktail'), pansies (Viola × wittrockiana `Atlas Purple'), petunias (Petunia hybrida), and impatiens (Impatiens wallerana `Lipstick') were determined by comparing aboveground dry weight to control plants after exposure to endothall in irrigation water. The objective was to determine if endothall concentrations used for aquatic weed control were phytotoxic to ornamental plants. Plants were irrigated every other day for 6 days in Expt. 1 with constant concentrations of endothall, and for 8 days in Expt. 2 with decreasing concentrations of endothall. Concentrations causing a 10% reduction in dry weight (effective concentration: EC10) compared to control plants showed there was a wide range of tolerance among plants exposed to endothall in irrigation water in the two experiments. Begonias, pansies, and impatiens had the lowest tolerance to two formulations of endothall in irrigation water with EC10 values ranging from 2 to 4 mg·L–1 (ppm) a.i. (a.i. based on acid equivalence) in both experiments. Petunias, which were more tolerant to endothall, had EC10 values of 15 and 34 mg·L–1 a.i. in Expt. 1 and 11 and 20 mg·L–1 a.i. in Expt. 2 for the amine and dipotassium formulations of endothall, respectively. Endothall did abscise flowers on impatiens after irrigation with endothall at concentrations of 10 mg·L–1 a.i. and higher. Effects of endothall on begonias at concentrations close to the EC10 values (2 to 3 mg·L–1 a.i.) were limited to growth inhibition with no apparent desiccation or necrosis of plant tissue.