Influence of water quality on Glyphosate performance and evaluation of Enlist™ Weed Control Systems in Texas High Plains Cotton
Manuchehri, Misha Rose
The quality of water used as the spray carrier, tank-mix combinations, weed size at application, and appropriate tank cleanout procedures are four factors among many others that will impact the success of auxin-based weed control systems in cotton. Multiple trials were conducted near Lubbock, TX from 2012 to 2015 to evaluate these factors. In water quality studies, water source affected glyphosate control in three of six trials when evaluated 21 days after treatment. As expected, an increase in glyphosate rate increased weed control for all six trials. The addition of ammonium sulfate, a water conditioner, also increased weed control for all six trials. When considering weed management systems, numerous effective systems were identified; however, systems containing Enlist Duo® or 2,4-D choline early postemergence and mid-postemergence were among the most effective. These systems provided 85 to 97% control while systems that relied on glufosinate alone mid-postemergence only achieved 28 to 66% control. When evaluating Palmer amaranth, Russian-thistle, and kochia control in non-crop, single postemergence application studies, treatments that consisted of Enlist Duo® or 2,4-D choline alone or as part of a tank-mix combination were the most successful. The greatest level of weed control for all three weed species was achieved at the 3 to 5 cm timing; however, weed size was most critical for Palmer amaranth and Russian-thistle when compared to kochia. When examining spray drift and tank contamination of Enlist Duo® on non-tolerant cotton in the Texas High Plains, nine leaf cotton was more sensitive than cotton at first bloom. This research suggests that non-2,4-D tolerant cotton is extremely sensitive to 2,4-D injury and that predicting yield loss based on visual injury is unreliable. In order to minimize the risk of drift while using these new technologies, applicators must use appropriate spray nozzle and pressure combinations, tank-mix only with permissible partners, apply only when temperature, relative humidity, wind speed, and wind direction are suitable, and respect buffer zone requirements and sensitive habitats. Critical application requirements will be outlined on herbicide labels and industry websites.