Foliar washoff and runoff losses of lactofen, norflurazon, and fluometuron under simulated rainfall

Lactofen [(+/-)-2-ethoxy-1-methyl-2-oxoethyl 5-[2-chloro-4-(trifluoromethyl) phenoxy]-2-nitrobenzoate] washoff from velvetleaf (Abutilon theophrasti Medic.) and common cocklebur (Xanthium strumarium L.) foliage was investigated. Plants were sprayed with lactofen at 0.4 kg of ai ha-1 and subjected to 2.5 cm of rainfall in 20 min at 1 and 24 h after application (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(2H)-pyridazinone], and fluometuron [N,N-dimethyl-N'-[3-(trifluoromethyl) phenyl]urea] on a Bosket sandy loam soil in 2.24 m 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.). Norflurazon and fluometuron losses in runoff from no-crop residue trays were 4.4% and 0.8%, 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