About dicamba： Response of Strip-tilled Cotton to Preplant Applications of Dicamba and 2,4-D

BY： Alan C. York, A. Stanley Culpepper, and Alexander M. Stewart

Conservation tillage is being adopted by cotton(Gossypium hirsutum L.) growers across the southeastern United States. Glyphosate is commonly applied prior to planting to control winter vegetation, but preplant control of certain weeds, especially cutleaf eveningprimrose (Oenothera laciniata Hill), requires 2,4-D or dicamba mixed with glyphosate. A field experiment was conducted at seven locations to determine response of strip-tilled cotton to dicamba diglycolamine salt at 280 and 560 g acid equivalent (a.e.) ha-1 or 2,4-D dimethylamine salt at 530 and 1060 g a.e. ha-1 applied 1 to 6 wk before planting (WBP). These rates are 1 and 2 times the labeled rates. No adverse effects on cotton were noted when 2,4-D was applied 3 or more WBP. Visible leaf distortion on more than 10% of the seedlings and stand reduction was noted at 1 of 7 locations when 2,4-D was applied 2 WBP and at 2 of 7 locations when applied 1 WBP. Cotton yield was not reduced by 2,4-D at 530 g ha-1 at any application time, and it was reduced by 2,4-D at 1060 g ha-1 applied 1 WBP at 1 of 7 locations. Dicamba at 280 g ha-1 applied 3 or more WBP did not cause leaf distortion or affect stands. Leaf distortion on more than 10% of seedlings was noted at 1 of 7 locations with 280 g ha-1 dicamba applied 2 WBP, but yield was unaffected regardless of time of application. Dicamba at 560 g ha-1 applied 3 WBP caused leaf distortion on more than 10% of the seedlings and reduced yield at 1 of 7 locations. Cotton response to dicamba, but not 2,4-D, was generally correlated with rainfall between application and planting.



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