HERBICIDE RUNOFF FROM ORNAMENTAL CONTAINER NURSERIES

Runoff and pond water samples from a container nursery that recycles water for irrigation were tested for movement of herbicides from the site of application. Residues of oryzalin [4-(dipropylamino)-3,5-dinitrobenzene-sulfonamide], pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzamine]), and oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene], active ingredients in the granular formulations of Rout [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene+3,5-dinitro-N-4,N-4-dipropylsulfanilamide] and OH-2 (Ornamental Herbicide-2), were evaluated. Herbicides were applied at labeled rates and followed by irrigation. Water samples were collected, herbicides were extracted by solid phase extraction and analyzed by reverse phase high pressure liquid chromatography with ultraviolet (UV) detection. Maximum herbicide residues were detected within the first 15 min of water runoff; oryzalin residues were the greatest of the three herbicides evaluated (4 mg L(-1) water at 15 min) and showed rapid decreases thereafter. Herbicide residues detected in pond samples decreased over time until the detection limit was reached (2 wk following application). A microplot study was conducted to evaluate the effects of plastic, woven fabric or gravel bedcovers on herbicide movement. Plastic and fabric allowed greatest movement of oryzalin and pendimethalin, while gravel significantly retained and retarded movement of all three herbicides. Results indicate that bedcover composition plays a significant role in the movement of herbicide from the site of application. Release of active ingredient from granular formulations was evaluated; dinitroani-lines (oryzalin and pendimethalin) release faster than oxyfluorfen. Oryzalin in Rout was the most rapidly released, is the most water soluble, and 71% of total active ingredient was accounted for after 3 wk.