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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