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April 2002


A large number of commonly used pesticides are decomposed quite rapidly in water containing detectable amounts of alkalinity.  This decomposition is due to a reaction called alkaline hydrolysis in which the pesticide molecule is split by the water and converted to an inactive form.   The rate of decomposition is determined by the chemical make-up of the pesticide and is different for each compound.  The reaction in all cases proceeds more rapidly as the pH of the water increases (becomes more alkaline).  In Western Colorado where water supplies commonly approach a pH of 8, pesticide decomposition can proceed at a rate rapid enough to affect the degree of performance.

This decomposition can be slowed or prevented by adjusting (buffering) the pH of the spray solution to a range where pesticide stability is at a maximum.  For most pesticides, the optimum pH is in the range 4 – 6 (slightly acidic).



Attached is a list of commonly used pesticides and their optimum pH.  Post it on the wall of your spray shed and check it before you mix each tank!


Fortunately the solution (no pun intended) is easy and inexpensive.  The addition of an adjuvant to buffer the spray water will cure the problem.  Always add the buffering agent before you put in any pesticide.


Give us a call and we can discuss the various buffering agents available.




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