HERBICIDE RUNOFF FROM ORNAMENTAL CONTAINER NURSERIES

Runoff and pond water samples from a container nursery that recycles w ater for irrigation were tested for movement of herbicides from the si te of application. Residues of oryzalin 4-(dipropylamino)-3,5-dinitrob enzene-sulfonamide], pendimethalin -ethylpropyl)-3,4-dimethyl-2,6-dini trobenzamine]), and oxyfluorfen thoxy-4-nitrophenoxy)-4-(trifluorometh yl)benzene], active ingredients in the granular formulations of Rout b enzene+3,5-dinitro-N-4,N-4-dipropylsulfanilamide] and OH-2 (Ornamental Herbicide-2), were evaluated. Herbicides were applied at labeled rate s and followed by irrigation. Water samples were collected, herbicides were extracted by solid phase extraction and analyzed by reverse phas e high pressure liquid chromatography with ultraviolet (UV) detection. Maximum herbicide residues were detected within the first 15 min of w ater runoff; oryzalin residues were the greatest of the three herbicid es evaluated (4 mg L(-1) water at 15 min) and showed rapid decreases t hereafter. 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 f abric allowed greatest movement of oryzalin and pendimethalin, while g ravel significantly retained and retarded movement of all three herbic ides. Results indicate that bedcover composition plays a significant r ole in the movement of herbicide from the site of application. Release of active ingredient from granular formulations was evaluated; dinitr oani-lines (oryzalin and pendimethalin) release faster than oxyfluorfe n. Oryzalin in Rout was the most rapidly released, is the most water s oluble, and 71% of total active ingredient was accounted for after 3 w k.