2330 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA J. zyxwvutsrq Agric. Food Chem. zyxwvuts 1994, zyxwvut 42, 2338-2343 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONM Foliar Washoff and Runoff Losses of Lactofen, Norflurazon, and Fluometuron under Simulated Rainfall zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFED Krishna N. Reddy,* Martin A. Locke, and Charles T. Bryson Southern Weed Science Laboratory, Agricultural Research Service, U.S. Department of Agnculture, P.O. Box 350, Stoneville, Mississippi 38776 Lactofen [(~~-2-ethoxy-l-methyl-2-oxoethyl5-[2-chloro-4-(trifluoromethyl)phenoxyl-2-nitrobenzoatel washoff from velvetleaf zyxwvutsrq (Abutilon theophrasti Medic.) and common cocklebur (Xanthium strumarium L.) foliage was investigated. Plants were sprayed with lactofen at 0.4 kg of ai ha-l and subjected to 2.5 cm of rainfall in 20 min at 1 and 24 h after application zyxw (HAA). At 1 HAA, in both species, over 97% of lactofen was washed off from foliage. At 24 HAA, lactofen washoff ranged from 51% to 82% in both species. Runoff losses of lactofen, norflurazon [4-chloro-5-(methylamino)-2-[3- (trifluoromethyl)phenyl]-3(W)-pyridazinoneI, and fluometuron [N,N-dimethyl-N’-[3-(trifluoro- methy1)phenyllureal on a Bosket sandy loam soil in 2.24 m zyxwv x 1.22 m x 0.25 m fiberglass runoff trays with 1.1% slope were also studied. A rainfall of 2.5 cm in 20 min at 24 HAA generated 0.8 cm of runoff and contained 3.2% of applied lactofen. However, lactofen loss in runoff was reduced by 94% with a cover crop of Italian ryegrass (Lolium multiflorum Lam.) and crimson clover (Trifolium incarnatum L.1. Norflurazon and fluometuron losses in runoff from no-crop residue trays were 4.4% and OB%, respectively, when a rainfall of 3.8 cm in 30 min was applied at 24 HAA. No runoff was observed in cover-crop residue trays. More than one-third of the total loss of all herbicides occurred in the first liter of runoff. Keywords: Herbicides; lactofen; norflurazon; fluometuron; runoff]. foliar washoff]. water quality; plant residue; cover crop; sediment INTRODUCTION Crop losses due to weeds, insects, and plant pathogens are enormous, and without effective pest control strate- gies, crop production is unprofitable. Use of synthetic chemicals for pest control is increasing in both developed and some less well developed countries. In terms of usage, herbicides top the list of pesticides. In 1991, the total pesticide usage on 10 major crops in the United States was 217 000 000 kg of active ingredient (ai), of which 183 000 000 kg (84%) was herbicides (Antognini, 1993). Herbicides provide cost-effective, timely weed control and help farmers to be highly productive and remain economically viable. Herbicides will probably remain an integral part of modern agriculture since there are no cost-effective weed control alternatives on the horizon that are likely to completely replace herbi- cides (Duke, 1992). Off-target movement of herbicides from agricultural lands and its impact on the environment is a growing public concern. Increasing awareness of potential prob- lems associated with herbicide use has provided impetus for studying alternative practices that reduce herbicide use. Increasing crop residue can impede surface water flow, thereby reducing movement of herbicide in runoff (Brown et al., 1985; Beke et al., 1989; Wauchope et al., 1990). No-tillage is one management practice that can increase crop residue over conventional tillage systems (Sadeghi and Isensee, 1992; Burwell and Kramer, 1983). Raising a cover crop during fallow periods can also reduce runoff of pesticide and soil erosion. In any management system, rainfall can reduce the efficacy of pesticides by washing the material off of the plant foliage when applied to foliage (Bryson, 1987; *Author to whom correspondence should be ad- dressed. Reddy and Singh, 1992) or by decreasing the availability of pesticide for target weed uptake by causing pesticide runoff and leaching when applied to soil. Rainfall also causes movement of soil-applied pesticides in runoff and by leaching (Baldwin et al., 1975; White et al., 1976; Asmussen et al., 1977; Wauchope, 1978,1987b; Wau- chope and Leonard, 1980; Burwell and Kramer, 1983; Lichtenstein and Liang, 1987; Hubbard et al., 1989; Buttle, 1990; Wauchope et al., 1990). However, in some cases, moderate rainfall immediately after application of certain soil-applied herbicides is beneficial for her- bicide incorporation into the upper soil zone. The elapsed time between pesticide application and a rain- fall event can be critical to pesticide washoff, runoff, or leaching losses. Knowledge of herbicide foliar washoff and runoff loss is essential information for environmental modeling, for optimizing weed management, and in developing alter- nate production practices (Cooper and Lipe, 1992). Full- scale field experiments are difficult and time-consuming, but simulated rainfall applied to small trays or trays of soil can provide useful runoff data (Wauchope, 1987a,b). Likewise, a simulated rainfall applied to plants treated with herbicides can provide information on vulnerability of herbicides to foliar washoff (Bryson, 1987; Reddy and Singh, 1992). Norflurazon and fluometuron are used extensively for weed control in cotton and many other crops. Norflu- razon and fluometuron are applied to the surface of the soil and sometimes incorporated. Fluometuron is some- times applied to plant foliage. Lactofen is mostly applied to plant foliage in both cotton and soybean production (Weed Science Society of America, 1989). Chemical properties of these herbicides are shown in Table 1. Information on the effect of crop residue on runoff of lactofen, norflurazon, and fluometuron in a typical cotton soil in the Mississippi delta has not been This article not subject to US. Copyright. Published 1994 by the American Chemical Society