Experiments conducted in 2003 to 2005 at the University of Arizona Maricopa and Safford Agricultural Centers (MAC and SAC) investigated weed management in RR Flex cotton and the consequences of weed competition on yield. A sprayed variety trial was also conducted in 2005 at the MAC. Factors investigated included tillage, preplant incorporated or preemergence pendimethalin applications, rate and sequence of glyphosate applications, and glyphosate application method. The use of residual herbicide and the consequences of weed competition due to delaying the first post-planting glyphosate application were also investigated. Results indicated superior weed control resulted from preplant-incorporated pendimethalin applications and earlier topical glyphosate applications at rates greater than 0.75 lb ae/A (i.e., 1.5 lb ae/A). Weed competition from ivyleaf morningglory and Palmer amaranth reduced cotton yields when the first post-planting glyphosate application was delayed until after the first post-planting irrigation. Applying glyphosate with a broadcast boom equipped with drop tubes with double swivels in the center of the furrow that sprayed the bottom half of 10 node cotton provided weed control similar to the use of a nozzle arrangement similar to that in Redball 420 layby hoods. Residual herbicide (e.g. prometryn) applied at layby was necessary to protect cotton yield and avoid having morningglory vines on top of the cotton canopy at harvest. In a sprayed variety trial a MAC in 2005, 34 varieties of RR Flex cotton were sprayed topically at the 2 leaf growth stage, sprayed “sloppy” post-direct at the 11 node growth stage and at layby with glyphosate at 1.5 lb ae/A. No injury symptoms were noted following glyphosate applications and the varieties were ranked according to yield.