FOLIAR ABSORPTION AND TRANSLOCATION OF NICOSULFURON AND RIMSULFURON IN 5 ANNUAL WEED SPECIES

Ambrosia artemisiifolia L. (common ragweed) and Digitaria ischaemum Schreb. (smooth crabgrass) are not controlled by nicosulfuron and rimsulfuron at the highest recommended application rates, whereas Panicum miliaceum L. (wild prose millet), Amaranthus retroflexus L. (redroot pigweed) and Avena fatua L. (wild oat) are susceptible. The foliar absorption and translocation of C-14-nicosulfuron and C-14-rimsulfuron were studied in these weed species up to 48 h after treatment (HAT). Differences in herbicide uptake and translocation were not correlated with the species susceptibility. By 48 HAT, more than 50% of both herbicides remained on the treated leaf surface. Foliar absorption of rimsulfuron was greater than that of nicosulfuron in A. retroflexus, P. miliaceum and A. artemisillfolia. Most of the absorbed herbicide remained in the treated leaf of each weed species. Export of C-14 nicosulfuron ranged from 28 to 54% of that absorbed, in contrast to 15 to 39% for C-14-rimsulfuron. The absorption and translocation rates of both herbicides were highest within the initial 6 HAT, and decreased thereafter. Both herbicides showed approximately the same distribution pattern within each weed species.