Laboratory experiments with14C-herbicides were conducted with grain sorghum as an indicator species to determine the effects of imposed moisture stress on absorption, precent recovery, and acropetal and basipetal translocation of the butyl ester of fluazifop, the methyl ester of haloxyfop, the ethyl ester of quizalofop, and sethoxydim. Haloxyfop was the only herbicide where recovery decreased between the 3-and 48-h interval. All plants absorbed more of the herbicide at the 48-h interval than at the 3- or 6-h interval under both stressed and non-stressed conditions. Increased drought stress caused more acropetal movement with fluazifop and sethoxydim and less acropetal movement with quizalofop at the 3-h interval. Basipetal transloation, although different among herbicides, responded similarly to imposed moisture stress, which decreased basipetal translocation approximately 19%.

The effects of temperature, relative humidity (RH) and light on absorption and translocation of14C-glyphosate [N-(phosphonomethyl)glycine] in common bermudagrass [Cynodon dactylon(L.) Pers. ‘Common’] and the effect of temperature and stage of growth on glyphosate activity in horsenettle (Solanum carolinenseL.) were determined.14C-glyphosate was used to evaluate the absorption and translocation of foliar-applied herbicide in bermudagrass plants grown at 22 or 31 C and 35 or 80% RH and absorption in excised leaf tips and stem sections. Autoradiography of bermudagrass indicated that downward translocation of14C was extensive with large accumulations in new roots and rapidly growing stolons. RH of 35% decreased14C-glyphosate translocation to the untreated foliage of plants grown at 31 C as compared to 80% RH. RH of 35% also decreased the translocation of14C to the rhizomes and roots of plants grown at 22 C. The absorption of14C was greater in excised leaf tips than stem sections and was greater in the light than in the dark. Horsenettle plants grown at 32 C had shoots which were more rapidly killed by glyphosate but had more regrowth than plants treated at 13 C. Shoots of plants treated while blooming were also more rapidly killed than those treated in the prebloom stage of growth, but the regrowth was not significantly different.

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Seedlings of winged elm (Ulmus dataMichx.), bur oak (Quercus macrocarpaMichx.), black walnut (Juglans nigraL.), eastern redcedar (Juniperus virginianaL.), and loblolly pine (Pinus taedaL.) were treated in nutrient solution with ring-labeled14C-tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} or14C-hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione]. Four hours later,14C was detected in all sections of winged elm treated with14C-tebuthiuron and14C-hexazinone. Root absorption of the tebuthiuron label by the other species occurred in the order: loblolly pine > bur oak > black walnut = eastern redcedar. The sequence of14C-hexazinone absorption was: loblolly pine > black walnut ≥ bur oak = eastern redcedar. Foliar accumulation of the tebuthiuron label occurred in the order: bur oak > loblolly pine > eastern redcedar = black walnut, whereas the sequence with hexazinone was loblolly pine > bur oak > black walnut = eastern redcedar. The presence of the three metabolites of hexazinone in loblolly pine suggests that it may be resistant to hexazinone as a result of its ability to degrade hexazinone rather than its ability to limit uptake.

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