Effect of pyrithiobac, MSMA, and DSMA on cotton (Gossypium hirsutum L.) growth and weed control

Field experiments were conducted at one location in Georgia (1994) and at two locations in Alabama (1994 and 1995) to evaluate the effects of MSMA or DSMA plus pyrithiobac applied postemergence (POST) in cotton. Pyrithiobac at 0.07 kg ai/ ha was applied POST alone or in combination with MSMA at 1.1 kg ai/ha or DSMA at 1.7 kg ai/ha at the pinhead square stage of cotton growth. Cotton was tolerant to the POST applications of pyrithiobac. Adding MSMA or DSMA to pyrithiobac injured cotton similar to MSMA or DSMA applied alone. Plant mapping data indicated that all treatments had no effect on height: node ratio, reproductive or vegetative node production, or square retention at the first or second fruiting position. Cotton maturity response to MSMA and DSMA ranged from no effect to delayed maturity. Adding DSMA to pyrithiobac increased Florida beggarweed and common cocklebur control over pyrithiobac applied alone in 1995 but did not increase control in 1994. Adding DSMA to pyrithiobac increased sicklepod control over pyrithiobac applied alone in the three site years it was rated in the Alabama tests. Where sicklepod is present, the addition of an arsenical herbicide to pyrithiobac will generally increase control but has the potential to delay maturity and decrease cotton yield equal to the arsenical herbicide applied alone.