Does Reverse Osmosis Water Affect Glyphosate Efficacy?

Water is the main carrier used in most herbicide applications. The quality of water plays a critical role in the success or failure of herbicide treatments, especially for weak acid herbicides such as glyphosate. In an attempt to offset potential antagonism of herbicides due to poor water quality, systems utilizing reverse osmosis (RO), a filtration process to remove dissolved inorganic solids from water, are being used by some growers in the Texas High Plains. Defining the role of water quality on glyphosate efficacy is important due to its increased use over the past 15 years. The effects of water quality and water conditioning agents on glyphosate efficacy were assessed in six field trials established near Lubbock, TX in 2012 and 2013. Test plants included volunteer winter wheat (Triticum aestivum L.), Palmer amaranth (Amaranthus palmeri S. Wats.), and kochia (Kochia scoparia L.). All trials were organized in a randomized complete block design with four replications. Five water samples, ranging in cation concentrations of 519-1,046 ppm, were selected from a collection of 23 wells throughout the Texas High Plains. The selected five sources plus a RO water source were used as carriers for the following four herbicide treatments: glyphosate applied alone at 0.43 and 0.86 kg ae ha^-1 and glyphosate applied at 0.43 and 0.86 kg ae ha^-1 with dry ammonium sulfate (AMS) at 20.37 g L^-1. Injury was recorded at 14, 21, and 28 days after treatment.