Cloransulam absorption, translocation, and efficacy on common broadleaf weed species

Field and laboratory studies were conducted to evaluate herbicide efficacy, absorption, and translocation of cloransulam within broadleaf weeds. Control of morning-glory species and velvetleaf with cloransulam was dependent upon application rate and timing. A reduced rate of cloransulam (9 g ai ha(-1)) was as effective as the labeled rate (18 g ha(-1)), when applications were targeted to small to midsize morningglory and velvetleaf. Prickly sida, hemp sesbania, and sicklepod were suppressed by cloransulam. Contour maps predicted accurately weed control for all species except tall morningglory. Cloransulam absorption and translocation provided some information about tolerance mechanisms. Susceptible species, entireleaf morningglory and velvetleaf, both rapidly absorbed C-14-cloransulam. Absorption in the more tolerant velvetleaf was 20% lower than entireleaf morningglory at all harvest times. Absorption of C-14-cloransulam in prickly sida was only 26% 6 h after treatment, and absorption did not increase with time. Differences in cloransulam absorption and translocation partially explained differences in susceptibility among some weed species but not others.