Droplet Size Impact on Efficacy of a Dicamba-plus-Glyphosate Mixture

Abstract

Chemical weed control remains a widely used component of integrated weed management strategies because of its cost-effectiveness and rapid removal of crop pests. Additionally, dicamba-plus-glyphosate mixtures are a commonly recommended herbicide combination to combat herbicide resistance, specifically in recently commercially released dicamba-tolerant soybean and cotton. However, increased spray drift concerns and antagonistic interactions require that the application process be optimized to maximize biological efficacy while minimizing environmental contamination potential. Field research was conducted in 2016, 2017, and 2018 across three locations (Mississippi, Nebraska, and North Dakota) for a total of six site-years. The objectives were to characterize the efficacy of a range of droplet sizes [150 µm (Fine) to 900 µm (Ultra Coarse)] using a dicamba-plus-glyphosate mixture and to create novel weed management recommendations utilizing pulse-width modulation (PWM) sprayer technology. Results across pooled site-years indicated that a droplet size of 395 µm (Coarse) maximized weed mortality from a dicamba-plus-glyphosate mixture at 94 L ha–1. However, droplet size could be increased to 620 µm (Extremely Coarse) to maintain 90% of the maximum weed mortality while further mitigating particle drift potential. Although generalized droplet size recommendations could be created across site-years, optimum droplet sizes within each site-year varied considerably and may be dependent on weed species, geographic location, weather conditions, and herbicide resistance(s) present in the field. The precise, site-specific application of a dicamba-plus-glyphosate mixture using the results of this research will allow applicators to more effectively utilize PWM sprayers, reduce particle drift potential, maintain biological efficacy, and reduce the selection pressure for the evolution of herbicide-resistant weeds.

Physicochemical properties, droplet size and volatility of dicamba with herbicides and adjuvants on tank-mixture

“…However, it was observed that similar sizes increased drift 12 . Droplet sizes close to 620 µm were recommended as weed control was maintained above 90% 12 .…”

“…Other researchers have also observed that dicamba and glyphosate mixture increased the presence of dicamba in air by 3 to 9 times, with a decrease occurring only at temperatures below 15 °C 11 . In another case, studying the efficacy of dicamba in relation to the droplet size, researchers found that 395 µm droplet size achieved better weed control than other droplet sizes 12 . However, it was observed that similar sizes increased drift 12 .…”

“…In another case, studying the efficacy of dicamba in relation to the droplet size, researchers found that 395 µm droplet size achieved better weed control than other droplet sizes 12 . However, it was observed that similar sizes increased drift 12 . Droplet sizes close to 620 µm were recommended as weed control was maintained above 90% 12 .…”

Evaluation of optimal droplet size for control of Palmer amaranth (Amaranthus palmeri) with acifluorfen

“…Smooth-term estimated degrees of freedom (EDF) and deviance explained values are shown in Table 3. A smooth-term EDF of 1 indicates minimum GAM model fluctuation and characterizes a linear model (Butts et al 2018(Butts et al , 2019a(Butts et al , 2019c. Deviance explained values provide a model-fitting estimation between predicted values and actual observations, with greater percentages representing an overall better model fit.…”

“…Prior to herbicide application, 10 plants per plot were tagged at the soil surface for aboveground biomass evaluation. To facilitate evaluation of Palmer amaranth control in response to droplet size, plants were allowed to grow up to 15 cm (Butts et al 2018(Butts et al , 2019a(Butts et al , 2019c. Rulers were used to ensure that tagged plants did not exceed 15 cm in height.…”