Effects of Low Rates of Dicamba Herbicide Overspray on Susceptible Cotton at Various Timings in South and Eastern Texas

Several trials were established in 2016 in the Southern and Eastern portions of Texas on non-dicamba tolerant cotton to assess the effects from a simulated improper herbicide tank cleanout of the herbicide dicamba.  This paper summarizes the results from two of the locations, Corpus Christi and College Station.

Dicamba was over sprayed onto the cotton at one of 4 timings, first square, first spare plus 2 weeks, first flower and first flower plus two weeks.  Rates of dicamba were based off of fractions of the standard rate of 16 oz/a (standard rate=x) and were as follows, 1/10x, 1/50x, 1/100x and 1/500x,   These rates correspond to various scenarios where the chemical may have not been fully cleaned out of a commercial sprayer before the sprayer was re-filled with another crop protection product and then over sprayed across the susceptible, non-dicamba tolerant, cotton variety.  The objectives of this study were to determine what types of physical damage and yield impact can be expected from different rates of dicamba herbicide accidently over sprayed onto a susceptible cotton variety at various stages of its development.