FRUITING RESPONSE OF COTTON (GOSSYPIUM-HIRSUTUM) TO PYRITHIOBAC

Field experiments were conducted in 1991 and 1992 near Stoneville, MS and Greenville, MS, to determine the impact of pyrithiobac on cotton f ruiting, maturity, and yield. Trials were conducted in areas maintaine d weed-free with standard production practices to optimize yields. Pyr ithiobac was applied at 105 or 210 g ae/ha either PRE or POST to cotto n in the cotyledon to 2-leaf, 5- to 7-leaf, and matchhead-square (MHS) stages of growth. At one location, monosodium salt of methylarsonic a cid (MSMA) and fluometuron plus MSMA were applied as standard comparis ons. At the Stoneville location, injury I wk after treatment (WAT) wit h pyrithiobac ranged from 2.5% with 105 g/ha applied at cotyledon to 2 -leaf to 26% with 210 g/ha applied at MHS. Injury was transient in nat ure and was rarely detectable 4 wk after treatment in either year. Inj ury was not evaluated at the Greenville location. At Stoneville, a red uction in height occurred with MHS applications of pyrithiobac and MSM A. There was no reduction in yield for any treatment compared to the u ntreated check in 1991 at Stoneville and in both years at Greenville. In 1992 at Stoneville, treatments of 210 g/ha pyrithiobac, MSMA, and f luometuron plus MSMA at all application timings reduced yield. Pyrithi obac at 105 g/ha applied PRE also reduced yield. Greatest yield loss o ccurred with treatments of MSMA applied at MHS. There were no yield re ductions at either location with postemergence application of 105 g/ha pyrithiobac.