Preemergence/postemergence pyrithiobac combinations control red morningglory and devil's-claw in cotton
Osborne, Toby Shane
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Field experiments in 1997 and 1998 evaluated cotton weed control and yield comparing a herbicide program utilizing sequential preemergence (PRE) and postemergence (POST) pyrithiobac combinations to standard PRE treatments of prometryn or diuron. At 90 days after planting (DAP), PRE applications of pyrithiobac at 0.04 kg ai/ha, prometryn at 0.9 or 1.34 kg/ha or diuron at 0.9 or 1.12 kg/ha controlled devil's-claw 18 to 47% in 1997 and 0% in 1998 and red morningglory 8 to 29% in 1997 and 2 to 17% in 1998. PRE applications of pyrithiobac at 0.05 or 0.07 kg/ha applied alone or in combination with diuron at 0.9 or .12 kg/ha or prometryn at 0.9 or 1.34 kg/ha controlled devil's-claw 53 to 75% in 1997 and 0 to 25% in 1998 and red morningglory 40 to 75% In 1997 and 18 to 47% in 1998. In both years, any PRE application followed by (fb) pyrithiobac applied POST controlled devil's-claw and red morningglory 80 to 100% at 90 days after planting. Devil's-claw infested plots that received PRE applications of pyrithiobac alone at 0.07 kg/ha or In combination with prometryn or diuron produced 383 to 556 kg llnt/ha in 1997 and 179 to 333 kg/ha in 1998. Plots receiving sequential applications of pyrithiobac alone or in combination with prometryn or diuron applied PRE yielded 517 to 657 kg lint/ha in 1997 and 404 to 855 kg/ha in 1998. Red morningglory infested plots that received pyrithiobac applied PRE at 0.05 or 0.07 kg/ha alone or in combination with prometryn at 0.9 or 1.34 kg/ha or diuron at 0.9 or 1.12 kg/ha produced 97 to 290 kg lint/ha in 1997 and 312 to 419 kg/ha n 1998. Sequential applications of pyrithiobac alone in 1997, produced 240 to 261 kg lint/ha in 1997; however, 532 to 560 kg lint/ha was harvested from these plots in 1998. Plots that received sequential applications of pyrithiobac including prometryn or diuron applied PRE yielded 364 to 411 kg lint/ha in 1997 and 851 to 927 kg lint/ha in 1998. This research indicated that sequential pyrithiobac applications controlled intense populations of red morningglory and devil's-claw more effectively than any treatment observed. PRE combinations of pyrithiobac plus prometryn or diuron improved devil's-claw and red morningglory control over prometryn, diuron or pyrithiobac alone; however, this control diminished to unacceptable levels by late season. Pyrithiobac plus diuron fb pyrithiobac or pyrithiobac plus prometryn fb pyrithiobac provided the greatest weed control, the highest cotton yields, and the greatest partial net returns to herbicide costs in both red morningglory and devil's-claw infested plots.