Penn State Extension is delivering an important message to pesticide applicators in Pennsylvania this year on the impact of water quality on pesticide performance.

Pesticide applicators each year look to Penn State Extension to learn of new research information and to obtain pesticide recertification credits to maintain their applicator licenses with the PA Department of Agriculture.

A water presentation was created by Fred Whitford at Purdue Extension and adapted for Pennsylvania by Bill Riden in the Pesticide Education Program at Penn State. In many cases, water makes up ninety-five percent of the total pesticide spray mix and is the foundation of the application. T

he quality of the water the applicator uses can affect the efficiency of the spray material. Yet few people consider the impact that the quality of the water can have on the spray product.

The pH of the water is a main concern due to a process called alkaline hydrolysis. This is a chemical reaction that occurs when some pesticides in the presence of alkaline water, or water with a pH above 7.0, degrade or lose their effectiveness. Many pesticides are formulated at a pH of 4.0 to 6.5 or slightly acidic.

The half-life of a product means the amount of time that is needed for one half of the substance to break down. The herbicide Flumioxazin, for example, is very stable at a pH of 5, but at a pH of 7 the half-life is 24 hours, and at a pH of 9 the half-life drops to only 15 minutes.

Extension Water Resources Educator, Jim Clark, was recently involved with a project in North Central Pennsylvania that tested 689 private water supplies. The low pH in this project was 3.0 and was found in Clearfield County, but the high pH of 8.79 was found in neighboring Jefferson County.

An important question for applicators is; what is the pH of the water that you are using to mix up your spray application and is it affecting the efficiency of the pesticide product you are using?

One other aspect of water quality covered in the presentation is the amount of total suspended solids in the water. This is the amount of material that is floating or suspended in your water. Usually the total suspended solids level in water will be higher in surface water sources such as ponds, rivers, or ditches.

Filters can remove this debris from water, and prevent spray nozzles from plugging up. However, there can be very small material such as salt, clay, and organic matter suspended in the water and these will settle to the bottom of the tank if they are left undisturbed.

It can be surprising what settles out of water, if you take a glass of water and leave it on the shelf for a few weeks. This turbid water is important because pesticides have the ability to adsorb or stick to soil particles and other particles suspended in water.

The pesticide product that adsorbs to these particles is not available to do what is expected and desired in a spray application and the efficiency of the spray application is decreased. This clearly describes why it is so important to properly clean out spray tanks between applications, as well as, check the total suspended solids level in the source water.

Twenty-four percent or 166 of the 689 of the private water samples, in the testing project referenced before, were found to be above the turbidity standard of 1 NTU (Nephelometric Turbidity Units).

Pesticide applicators should be aware that water quality issues can mean reduced pesticide performance even if the equipment is calibrated and the application is perfect. It has been proven in research, and now shared by extension, that poor water quality can have a negative effect on certain families of pesticides.

A small amount of effort to have your water tested is rather cheap insurance to ensure that products perform as promised and deliver the expected results.

(Written By: Jim Clark, Extension Educator, McKean County, and reprinted from Penn State Extension’s Watershed Winds newsletter.)

4/8/2013