Evaluation of WideStrike (R) Flex Cotton Response to Over-the-Top Glufosinate Tank Mixtures

Field studies were conducted in Louisiana, Mississippi, and Tennessee during 2010 to investigate tolerance of 'PHY 375 WRF' and 'PHY 485 WRF' cotton to post applications of glufosinate and glufosinate tank mixtures. Glufosinate, glyphosate, S-metolachlor, and dimethoate were applied alone and in all possible combinations of the four pesticides to two-leaf cotton. Glufosinateonly treatment injured cotton 18%, which was much higher than injury from S-metolachlor-, dimethoate-, and glyphosate-alone treatments. The tank mixture that delayed maturity the greatest was glufosinate plus S-metolachlor. The lowest yielding treatments were glyphosate plus glufosinate plus dimethoate plus S-metolachlor, glufosinate plus glyphosate plus S-metolachlor, and glufosinate plus glyphosate plus S-metolachlor. Yields were also reduced following application of glufosinate plus S-metolachlor and glufosinate plus glyphosate. When all tank mixtures that contained both glufosinate and Smetolachlor were compared to all tank mixtures containing glyphosate and S-metolachlor, injury was greater (21 vs 8%) with glufosinate-based treatments. This resulted in delayed maturity (4.1 vs 3.5 node above cracked boll [NACB]) and lower yield (1100 vs 1230 kg ha(-1)) for glufosinate-based treatments. When we compared all the treatments that contained both glufosinate and dimethoate to those that contained both glyphosate and dimethoate, injury was greater (18 vs 5%), which resulted in delayed maturity (4.1 vs 3.3 NACB) but did not decrease yield. This data would suggest that growers should be cautious combining glufosinate with other pesticides and applying to WideStrike r cotton.