FACTORS AFFECTING BENFURESATE ACTIVITY AGAINST PURPLE NUTSEDGE (CYPERUS-ROTUNDUS L)

Benfuresate (2-3-dihydro-3,3 -dimethylbenzofuran-5-yl ethanesulfonate) is a selective herbicide for the control of purple nutsedge in cotton. Under outdoor conditions, purple nutsedge was sensitive to benfuresate incorporated in soil up to eight days after initiation of shoot sprouting from the tuber. Older seedlings recovered from the damage. During the period of susceptibility to benfuresate, young shoots more sensitive than the roots. Under controlled environmental conditions, benfuresate applied directly to apical buds developing from the tuber caused severe damage to the treated bud and induced abrupt development of axillary buds. Negligible amounts of the applied herbicide were translocated from the treated part to the other buds and roots. Application of the herbicide to fully developed leaves had no effect, probably because of its rapid metabolism and low basipetal mobility. Its relatively high volatility may also contribute to its low foliar post-emergence activity. Tubers also absorbed herbicide vapours. Root uptake of C-14-benfuresate resulted in a rapid accumulation of C-14 in the shoot, which had no effect on the purple nutsedge plant, regardless of concentration. The herbicide is rapidly converted, mainly to a non-phytotoxic polar product. These results may explain the high sensitivity of the weed to benfuresate at early growth stages, and the lack of sensitivity in mature plants.