Droplet Size Impact on Acifluorfen and Lactofen Efficacy for Palmer Amaranth (Amaranthus Palmeri) Control

Experiments were conducted in 2016, 2017, and 2018 at Hood Farms in Dundee, MS, and the West Central Research and Extension Center in North Platte, NE to evaluate the influence of droplet size on lactofen and acifluorfen effectiveness for Palmer amaranth control. Lactofen was applied at 0.21 kg ai ha^-1 + Crop Oil Concentrate at 1% v/v and acifluorfen at 0.42 kg ai ha^-1 + Crop Oil Concentrate at 1% v/v using the following droplet sizes: 150 μm, 300 μm, 450 μm, 600 μm, 750 μm, and 900 μm. Prior to experiment initiation, droplet size spectra for each herbicide was characterized in a low speed wind tunnel at the Pesticide Application Technology Laboratory at University of Nebraska, North Platte, NE. Treatments were POST applied to 15 cm Palmer amaranth using a tractor mounted sprayer equipped with a CAPSTAN^® AG Pulse Modulated Sprayer and Wilger Precision Spray Technology Tips at 4.8 km per hour using a spray volume of 140 L ha^-1. Visual Palmer amaranth control was collected at 7, 14, 21, and 28 days after application. Fifteen plants per plot were tagged and used for dry biomass calculation at the end of the experiment. Data were subjected to analysis of variance using PROC GLM procedure in SAS^® Software v. 9.4 and means were separated using Fischer’s Protected LSD at α=0.05. Different droplet sizes of lactofen did not differ with respect to Palmer amaranth control, regardless of rating period. Acifluorfen applied using 300 μm droplets provided the greatest Palmer amaranth control, regardless of rating period. Furthermore, compared to 450 μm, acifluorfen applied with 300 μm provided a 25% increase in Palmer amaranth control.