Hard water – caused by the presence of dissolved cations such as calcium, magnesium and iron – affects about 85 percent of the country and has been shown to reduce the efficacy of glyphosate and other weak acid herbicides. The positively charged cations in hard water bind with the negatively charged glyphosate molecules, resulting in less-effective weed control.
Fortunately, there is a simple, inexpensive remedy. When ammonium sulfate is added to hard water, it breaks down into ammonium and sulfate. The negatively charged sulfate binds to the positively charged cations in hard water. Consequently, conditioning hard water with ammonium sulfate in a sprayer before adding glyphosate can improve herbicide uptake and efficacy.
Test your water to determine if and how much ammonium sulfate is needed. Water with a hardness of 200 ppm or more should be treated with ammonium sulfate. As a general rule of thumb, a readily available 51-pound bag of ammonium sulfate per 300 gallons of water is enough to combat issues with hard water.
In addition to hard water, other factors such as pH, turbidity and even water temperature can affect the performance of pesticides. You can learn more about this important but often overlooked issue by reading, The Influence of Spray Water Quality on Herbicide Efficacy.
Central Region Agronomists:
Bob Vavrek, regional director – bvavrek@usga.org
John Daniels, agronomist – jdaniels@usga.org
Zach Nicoludis, agronomist – znicoludis@usga.org
Information on the USGA’s Course Consulting Service
