Thiocarbamates for Selective Control of Purple Nutsedge in Arizona Cotton
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AbstractPurple nutsedge Cyperus rotundus is an important weed in cotton (Gossypium spp.) production in Arizona. It is estimated that 15% of the crop acreage is infested. The technology available for selective control of purple nutsedge is not adequate and the infestation level of this weed is increasing. In 1986, the thiocarbamate herbicides, vernolate (Surpass), EPTC (Eptam, Genep) and butylate (Swan +, Genate plus) were evaluated as preplant and postemergence incorporated applications for selective control of purple nutsedge in cotton. There were 25 different trials conducted in Arizona cotton fields. Butylate was more selective to seedling cotton than EPTC and vernolate but all were capable of unacceptable cotton injury. Where preplant irrigations require every furrow irrigation, this concentrated the thiocarbamates in the seed row and resulted in less selectivity. Preplant treatments controlled purple nutsedge for 1 or 2 postemergence irrigations. Postemergence applications were most effective following preplant treatments but were not consistent in controlling nutsedge season -long. This research indicates that purple nutsedge lowered yields only when the cotton was stunted in growth by severe early season infestations. Wherever cotton established dominance over the weeds, yields were not affected. Preplant applications of butylate, if carefully adjusted for the growing conditions, can provide early season control of purple nutsedge.