Amaranthus control in cotton can be difficult with the loss of glyphosate efficacy, especially in conservation-tillage cropping systems. Research was conduction from 2006 to 2008 at EV Smith Research Center, Shorter, AL, to determine the level of glyphosate-susceptible Amaranthus control provided by four initial tillage and herbicide treatments, including 1) moldboard plowing followed by a single-pass disking and field cultivation plus pendimethalin at 1.2 kg ai ha~(-1) preplant incorporation (PPI),2) two-pass disking followed by field cultivation plus pendimethalin at 1.2 kg ha~(-1) PPI, 3) no tillage including an application of pendimethalin at 1.2 kg ha~(-1) PRE, or 4) no tillage without pendimethalin in 2006. No further tillage practices or pendimethalin applications were utilized after study initiation. Initial tillage operations, including inversion with disking or disking twice, resulted in Amaranthus density of 4plants m~(-2) and 14 to 62 control. Subsequent applications of PRE herbicides included fluometuron at 1.68 kg ai ha~(-1) or prometryn at 1.12 kg ai ha~(-1) and provided 53 to 98 and 55 to 93 control, respectively, and reduced Amaranthus density compared to no PRE herbicide to < 2 plants m~(-2), regardless of tillage treatment. A POST application of glyphosate at 1.0 kg ae ha~(-1) improved control in conjunction with almost all treatments in each year. Results indicate that a one-time tillage operation followed by a return to reduced tillage may aid in the reduction of Amaranthus density when used with PRE-applied herbicides; however, this system will likely not provide adequate control when high population densities of glyphosate-resistant Amaranthus are present, thus highlighting the need for a highly efficacious POST herbicide system.
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