ABSTRACT

Field studies were conducted to examine the impact of weed competition on cotton from delaying the first glyphosate application in Roundup Ready Flex^® cotton. Studies were established at the Attapulgus Research Farm near Attapulgus, GA and the Plant Sciences Farm near Athens, GA in 2003. Cotton was exposed to 2, 3, 4, 5, and 6 weeks of weed competition after emergence with and without pendimethalin applied preemergence. At the Athens location, cotton mapping and yield data indicated no impact of weed competition. This is possibly due to lower than anticipated weed populations at this site. At the Attapulgus location, first and second position boll counts declined from 25 to 5 at nodes 11-15 in cotton exposed to 3 to 5 weeks of weed competition. Third position boll numbers declined at nodes 5-10, 11-15, and at all nodes >15. Seed cotton data were regressed against weeks of competition with associated weeds. When pendimethalin was applied PRE at 0.84 kg ai/ha, 80 kg seed cotton yield were lost for each week cotton was exposed to weed competition beyond three weeks after emergence. When pendimethalin was not applied, 107 kg seed cotton yield was lost for each week cotton was exposed to competition. These data indicate the need for growers to control weeds during early season cotton growth.