Influence of Water Quality and Ammonium Sulfate on Glyphosate Efficacy

Aims: The objectives of these studies were to 1) determine west Texas water hardness values, 2) determine if glyphosate efficacy is affected by water carrier source, 3) determine if there is a benefit using reverse osmosis water as the carrier when applying glyphosate, and 4) determine if ammonium sulfate will improve glyphosate control regardless of water quality.

Study Design: All trials were arranged in a randomized complete block design.

Place and Duration of Study: Four studies were conducted in 2012 near Lubbock, TX, two using winter wheat (Triticum aestivum L.) and two using Palmer amaranth (Amaranthus palmeri S. Wats.) as the target species. Two winter wheat studies also were conducted in 2013 near Lubbock, TX.

Methodology: Water from five pre-selected sources, ranging in total water hardness from 185 to 1046 ppm plus an RO water source (11 ppm), was used as carriers for the following four herbicide treatments: glyphosate applied at 430 and 860 g ae ha-1 with and without dry ammonium sulfate.The rate of AMS was 2 kg 100 L-1 of water.

Results: West Texas water hardness values were highly variable, ranging from 91 to 1046 ppm. Water source affected glyphosate control in seven of the ten assessments over six trials conducted in two years. The reverse osmosis water source (11 ppm) was the top performing water source or was in the top performing group of sources in five of six assessments where water source impacted results. However, in several instances, water sources with cation concentrations over 800 ppm also were in the top performing group of water sources.

Conclusion: In all assessments, glyphosate at 860 g ae ha-1 and ammonium sulfate improved glyphosate efficacy, regardless of plant species tested. Continued work needs to be conducted in order to further evaluate the use of reverse osmosis water as a spray carrier for glyphosate.