Influence of Cultivation Timing on Pyrithiobac Performance in Cotton (Gossypium hirsutum)1

Pitted morningglory control with norflurazon or fluometuron preemergence (PRE), each at 1.12 kg/ha, was 72% or less 14 d after a postemergence (POST) application of pyrithiobac in 1993 and 1994. Pyrithiobac POST at 70 g/ha following fluometuron or norflurazon PRE cultivated at any timing controlled pitted morningglory at least 76%. Pyrithiobac POST controlled common cocklebur equal to the weed-free in 1993 at 14 d after the POST application. In 1994, when rated 28 d after pyrithiobac POST, cultivation 3 d before a single application of pyrithiobac controlled less common cocklebur than any other herbicide treatment containing pyrithiobac. At 28 d after pyrithiobac POST, no treatment controlled common cocklebur as well as the weed-free. In 1993 and 1994, seed cotton yield was equal to the weed-free when pyrithiobac followed fluometuron PRE cultivated at any timing or a single application of pyrithiobac cultivated prior to 7 d after POST application.Nomenclature: Fluometuron, N,N′-dimethyl-N′-[3-(trifluoromethyl)phenyl]urea; norflurazon, 4-chloro-5-(methylamino)-2-(3-(trifluoromethyl)phenyl)-3(2H)-pyridazinone; pyrithiobac, 2-chloro-6-[(4,6-dimethoxy-2-pyrimidinyl)thio] benzoic acid, sodium salt; common cocklebur, Xanthium strumarium L. #3 XANST; pitted morningglory, Ipomoea lacunosa L. # IPOLA; cotton, Gossypium hirsutum L. ‘DES-119’.Additional index words: Fluometuron, norflurazon, Ipomoea lacunosa, Xanthium strumarium, IPOLA, XANST.Abbreviations: ALS, acetolactate synthase (EC 4.1.3.18); DAPA, days after POST application; DBPA, days before POST application; DREC, Delta Research and Extension Center; fb, followed by; IAPA, immediately after POST application; POST, postemergence; PRE, preemergence; PSRC, Plant Science Research Center; SWSRU, Southern Weed Science Research Unit Farm.