Sprayer hygiene and concerns of off-target injury from auxin herbicides have increased in recent years. New auxin tolerant crops have broadened the use patterns of these herbicides. Therefore, experiments were conducted across two locations in Mississippi in 2016, 2017, and 2018 to evaluate sprayer cleanout procedures to aid in dicamba removal. Standard sprayer cleanout consisted of a triple rinse of 10% tank volume, with either a tank cleaner or ammonia added in the second rinse. Samples collected in each rinse step for all treatments were applied to actively growing soybean and dicamba concentration quantified with HPLC. Experiments were conducted to determine if various tank cleaners and ammonia produce visual injury when applied to actively growing soybean and cotton alone and in conjunction with glyphosate. No tank cleaner caused visual injury nor affected plant heights or yield. Furthermore, experiments were conducted to evaluate tank cleaner effectiveness to remove dicamba utilizing the standard cleanout procedure, with increased rinse volumes, sequence of water and tank cleaner rinses, and cleanout effectiveness following durations of idle time from application to cleanout. No tank cleaner provided greater dicamba removal, with all cleaners performing the same as cleanouts utilizing water alone. Increasing rinse volumes did not positively affect dicamba removal compared to 10% rinse volumes. Multiple rinse steps utilizing a tank cleaner or altering the standard cleanout procedure utilizing a water-tank cleaner-water rinse sequence did not result in greater dicamba removal from contaminated sprayer systems. Finally, increases in time between contamination with dicamba and cleanout did not negatively influence dicamba removal using the standard cleanout procedure.

Field and greenhouse experiments were conducted to determine the effect of auxin injury on soybean and cotton due to spray hose material, formulation and cleanout procedures on auxin equipment cleanout. Visual estimations of injury (VEOI) in wheat, height reduction, and yield reduction due to rimsulfuron and glyphosate titration was higher when compared to rimsulfuron only treatments with respect to 1/2X through the 1/256X treatments. Sequestration of 2,4-D within agricultural hose types did differ due to hose type and is confirmed by analytical testing, but field observation of wheat did not show differences among treatments due to VEOI, height reduction or yield reduction. Using soybean as a bio-indicator, differences did occur with respect to dicamba sequestration in agricultural hose types with respect to VEOI, height reduction, node reduction, yield reduction and ppm analyte retained. Results indicate chemical makeup of hose type in determination of ppm analyte dicamba retained. Cleaning procedures of water or ammonia do not prove to be different with respect to VEOI, height reduction, yield reduction or ppm analyte retained. Sequestration of 2,4-D within valved manifold systems and using water or ammonia as cleanout procedures in conjunction with rinse procedures did not show differences with respect to VEOI, height reduction, nodes above cracked boll (NACB), yield reduction or ppm analyte retained. It was not until standard 2,4-D applications were applied in field experiments when differences were observed. Deactivation of dicamba and 2,4-D using the Fenton procedure within various rates, showed an interaction with respect to VEOI, height reduction, node reduction, yield reduction and ppm analyte. Using soybean as a bio-indicator showed differences with the Fenton procedure deactivating the dicamba analyte in the 1/16X, 1/64X and 1/256X rate with respect to VEOI, height reduction, node reduction, yield reduction and ppm analyte retained. Using cotton as a bio-indicator showed differences with the Fenton procedure deactivating the 2,4-D analyte in every rate with respect to VEOI, height reduction, yield reduction and ppm analyte.

Seed companies have developed novel weed control technologies to combat herbicide-resistant (HR) weeds based on the use of new genetically-modified (GM) crop cultivars and auxin herbicide formulations. These herbicides can variably affect the growth and yield of susceptible cotton even at low concentrations depending on growth stage at exposure. As such, research was conducted in each of two locations in Mississippi in 2014, 2015, and 2016 to determine the cotton growth stage most susceptible to injury and yield effects from simulated misapplications of sub-lethal 2,4-D or dicamba concentrations. Results indicate that generally a decrease in yield partitioned on lower nodes and inner positions was accompanied by a compensatory increase in yield partitioned on vegetative branches and aborted terminals. However, the magnitude of these yield effects differed based on growth stage at exposure and based on which herbicide was used.