Weed Control Programs for Minimum-Tillage Cotton (Gossypium hirsutum)

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Abstract
Eleven herbicide systems were evaluated from 1981 to 1983 for cotton (Gossypium hirsutumL. ‘Stoneville 825’) planted no-till directly into cover crops or winter fallow and for cotton planted following conventional tillage. Herbicide systems consisted of paraquat (1,1’-dimethyl-4,4’-bipyridinium ion) or glyphosate [N-(phosphonomethyl)glycine] and/or residual herbicides applied prior to crop emergence. Some systems also included early postemergence or postemergence-directed applications. Cover crops were crimson clover (Trifolium incarnatumL.), hairy vetch (Vicia villosaRoth.), and rye (Secale cerealeL.). Soil cover in fallow treatments was comprised mainly of cotton stalk residue. Conventional tillage and seedbed preparation included fall moldboard plowing and spring disking/smoothing. Treatments were maintained in the same site each year. Order of cover crop susceptibility to herbicides applied prior to crop emergence was rye>clover>vetch. In 1981, all residual treatments except cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl]amino]-2-methylpropanenitrile} alone prior to crop emergence provided better than 80% control of annual weeds. In subsequent years only systems that included applications prior to crop emergence and postemergence-directed herbicides provided acceptable control. From 1981 to 1983, annual grasses increased 20- to 100-fold for systems in which control was poor. Weed control was generally superior in conventional tillage. Vetch adversely affected cotton stands in all 3 yr. Also, in 1982, reduced cotton stands resulted from cyanazine treatments applied prior to crop emergence in clover, vetch, and fallow. Cotton yields were affected by cover dessication, annual weed control, and cotton stands. Buildup of annual weeds reduced yields to near zero for some treatments in 1983.