Field trials were conducted near Lubbock, TX in 2013, 2014, and 2015 to evaluate non-2,4-D tolerant cotton response to low rates of glyphosate plus 2,4-D choline (Enlist Duo™). Cotton was treated with five rates of Enlist Duo™ (0.0183, 0.183, 1.83, 18.3, and 183 g ae ha-1) at two application timings (nine leaf and first bloom). These rates correspond to contamination rates of 0.0008, 0.008, 0.08, 0.8, and 8%, respectively. Visual cotton injury, boll retention, lint yield, and fiber properties were recorded. When averaged over contamination rates, visual injury following applications made to nine leaf cotton was greater than for first bloom cotton in three of three years and yield loss was greater when applications were made to nine leaf cotton when compared to first bloom cotton in two of three years. Averaged over application timing, lint yield in 2013, 2014, and 2015 following Enlist Duo™ contamination rates of 0.0008 and 0.008% were not different than the nontreated control while contamination rates of 0.08, 0.8, and 8% decreased yield by 3 to 20, 45 to 58, and 80 to 96%, respectively. Contamination rates of 0.0008, 0.008, 0.08, and 0.8% rarely affected fiber quality; however, a contamination rate of 8% frequently decreased micronaire, fiber length, fiber length uniformity, and fiber strength.
This decrease in fiber quality also resulted in a reduction in cotton loan value and potential financial return. For the 0.8% contamination rate, although decreases in fiber quality parameters were not observed, significant reductions in financial return were present due to yield loss caused by Enlist Duo™ injury.