July 2013

Just the Facts: Water Quality’s Impact on Herbicide Performance

Herbicide applicators are trained to know the influence that certain factors can have on the effectiveness of the application — things like application timing, equipment calibration and selection of the proper herbicide for the vegetation being treated. One factor often overlooked is water quality.

Water is often 95 percent or more of the total herbicide spray solution. So it makes sense that water quality could impact the effectiveness of the herbicide application.

This was the focus of a publication by Purdue Pesticide Programs, a function of the Purdue University Cooperative Extension Service. The publication is called The Impact of Water Quality on Pesticide Performance.

Poor water quality can have adverse effects.
What kinds of problems can poor water quality cause in a herbicide solution? For one, if water contains high levels of acidity and/or dissolved minerals, these may interact with the active and/or additive ingredients in the herbicide formulation. Poor-quality water also can adversely influence the herbicide by reducing the solubility and decreasing absorption by the target plant, resulting in poor performance.

These problems might not always drastically reduce performance, but even a slight drop may be enough to cause significant control issues when treating particularly difficult species, or species that are tolerant to certain herbicides. And if this happens, water quality often is overlooked as the culprit. The immediate suspects are factors such as improper tank-mixing, poor weather conditions at the time of application or perhaps the herbicide used.

Testing water is important.
The publication makes the case for testing your water before making a tank mix. Things to measure include iron levels, pH and water hardness. There are essentially two options for testing your water: Hire a professional vendor or purchase a do-it-yourself water-testing kit. The route selected probably will be influenced by the water source.

If an operation is getting the majority of the water used in applications from the same main source, it’s fairly simple to bring in a professional to determine the water quality before the season starts.

Selecting the do-it-yourself testing route makes more sense for those who are using multiple water sources from various areas and locations. These kits are readily available and usually involve using color-changing paper to document the pH, water hardness and iron levels.

Water quality problems can be solved.
The publication also recommends ways to solve water quality issues. It starts with reviewing the recommendations on the herbicide label. The label may specify pH levels needed, or it may warn about reduced effectiveness if mixed with water that is considered to have high hardness levels.

If the water doesn’t meet requirements, it may be necessary to add an adjuvant or it may require conditioning the water. A water conditioner can be added to the herbicide solution to eliminate problems with water hardness. A pH buffer can be used to raise or lower the water’s pH.

The full publication provides important details on the topic. To read it in its entirety, visit www.ppp.purdue.edu and click on “Extension publications” and then “Publications.”