Absorption, Translocation, and Degradation of Tebuthiuron and Hexazinone in Woody Species

Seedlings of winged elm (Ulmus data Michx.), bur oak (Quercus macrocarpa Michx.), black walnut (Juglans nigra L.), eastern redcedar (Juniperus virginiana L.), and loblolly pine (Pinus taeda L.) were treated in nutrient solution with ring-labeled 14C-tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} or 14C-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 with 14C-tebuthiuron and 14C-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 of 14C-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.