Tuesday, April 30, 2019

Pesticide Applications- Water Quality

Jesse Fulbright, MSU Liberty County Extension

It is not uncommon, according to an MSU Extension MontGuide, for Montana applicators to use water sources with pH levels higher than 8.0 and/or hardness ratings greater than 150 ppm.  This poor water quality can affect pesticide product performance, and as a result, product application rates often being raised, resulting in unnecessary losses in revenue.

In trying to work with water pH, remember that most insecticides, fungicides and herbicides are weakly acidic; that is when they are placed in water with a higher pH, over 7, they undergo degradation.  You can test your water with a litmus strip, or a pH meter.  Keep in mind that the pH of your water can vary with time and should be reassessed periodically.  Commercial buffers are available that can lower the pH of a spray solution for those weakly acidic pesticides.
Hardness, or hard water, refers to the presence of metals with a positive charge of more than 1, such as calcium, magnesium and iron.  The effect of water hardness is the further reduction of the effectiveness of weak acid pesticides, especially with a high pH water.  Hardness can be reduced with the addition of dry ammonium sulfate at 8.5 to 17.5 lbs./100 gallons of water, or liquid fertilizers, such as a 10-34-0 at a rate of 1.25 to 2.5% per 100 gallons.  Performance might be further enhanced by the addition of a non-ionic surfactant.

Turbidity can also affect pesticide performance.  This is simply the haziness of a liquid caused by suspended particles, such as soil and organic matter.  Applicators can test water turbidity by dropping a quarter into a five-gallon bucket filled with water.  If the water is too cloudy to see the quarter, seek an alternative source of water for spray mixtures.
If you have questions about your water quality, I would encourage you to contact your local county Extension office for more information, or for a copy of the MontGuide, titled, “Pesticide Performance and Water Quality.”

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