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 benfuresa te incorporated in soil up to eight days after initiation of shoot spr outing from the tuber. Older seedlings recovered from the damage. Duri ng the period of susceptibility to benfuresate, young shoots more sens itive than the roots. Under controlled environmental conditions, benfu resate applied directly to apical buds developing from the tuber cause d severe damage to the treated bud and induced abrupt development of a xillary buds. Negligible amounts of the applied herbicide were translo cated from the treated part to the other buds and roots. Application o f the herbicide to fully developed leaves had no effect, probably beca use 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, whi ch had no effect on the purple nutsedge plant, regardless of concentra tion. The herbicide is rapidly converted, mainly to a non-phytotoxic p olar product. These results may explain the high sensitivity of the we ed to benfuresate at early growth stages, and the lack of sensitivity in mature plants.