DPX PE350, an experimental herbicide, has shown excellent potential for controlling a wide range of problem broadleaf weeds in cotton. PPI, PRE, and POST applications of DPX PE350 at 0.1 and 0.2 kg ai/ha were evaluated under weedfree conditions in 1991 and 1992 for effects on ‘Paymaster HS26’ cotton growth, yield, and fiber quality. In 1991, DPX PE350 applied PPI, PRE, or POST did not affect cotton population, height, yield, or fiber quality. In 1992, DPX PE350 applied PPI at 0.1 or 0.2 kg/ha or PRE at 0.2 kg/ha injured the cotton and reduced yield and micronaire value.

Horseweed is a major weed in conservation tillage production systems. Herbicides were evaluated for horseweed control at two growth stages, rosette and 10- to 15-cm tall. Horseweed was controlled at the rosette stage with the 2,4-D ester, 2,4-D amine, dicamba, 2,4-D plus glyphosate, and glyphosate. Higher rates were needed for control at the 10- to 15-cm stage. Paraquat did not effectively control horseweed at any stage.

Field experiments conducted in 1991, 1992, and 1993 evaluated Palmer amaranth and devil's-claw control and cotton injury with pyrithiobac applied 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 PPI or PRE injured cotton 9 to 11% 6 wk after treatment. Cotton recovered and no injury was observed 12 wk after treatment. Pyrithiobac applied 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/ha. Devil's-claw control with pyrithiobac was better with POST applications than PPI or PRE applications. Pyrithiobac applied POST at 140 g/ha controlled devil's-claw 83–97%. These studies indicate that pyrithiobac can effectively control Palmer amaranth and devil's-claw in cotton on the Texas Southern High Plains when applied at appropriate rates and timings.