PALMER AMARANTH (AMARANTHUS-PALMERI) AND DEVILS-CLAW (PROBOSCIDEA-LOUISIANICA) CONTROL IN COTTON (GOSSYPIUM-HIRSUTUM) WITH PYRITHIOBAC

Field experiments conducted in 1991, 1992, and 1993 evaluated Palmer a maranth and devil's-claw control and cotton injury with pyrithiobac ap plied PPI, PRE, or POST. Pyrithiobac at 36 or 71 g ae/ha applied PPI, PRE, or POST did not injure cotton. Pyrithiobac at 140 g/ha applied PP I or PRE injured cotton 9 to 11% 6 wk after treatment. Cotton recovere d and no injury was observed 12 wk after treatment. Pyrithiobac applie d PPI and PRE at 71 g/ha controlled Palmer amaranth at least 97% 6 wk after treatment. Palmer amaranth control with pyrithiobac applied POST was more variable and influenced by environmental conditions. Palmer amaranth control with 71 g/ha of pyrithiobac exceeded that with 36 g/h a. Devil's-claw control with pyrithiobac was better with POST applicat ions than PPI or PRE applications. Pyrithiobac applied POST at 140 g/h a controlled devil's-claw 83-97%. These studies indicate that pyrithio bac can effectively control Palmer amaranth and devil's-claw in cotton on the Texas Southern High Plains when applied at appropriate rates a nd timings.