Jun 12, 2012 – Water and Pesticides
QUESTION:
How much effect does the pH of the mixing water have on the efficacy of Bifen 7.9 and what is the ideal water pH for mixing with Bifen 7.9?
ANSWER:
It is probably a good idea to know in general what the quality is of the water used to dilute pesticide concentrates, and for that matter even the pH of the soils and other surfaces you apply the sprays to. Water that is high in alkalinity (a high pH) is more likely to affect chemical molecules than one that is slightly on the acid side (lower in pH). If my basic chemistry knowledge is still correct the scale of pH runs from 0 to 14, with 0 being extraordinarily acidic and 14 being terribly alkaline (also called "basic") and with 7 right in the middle as neutral. Plain, clean water is supposed to be right around 7.0, but when minerals are in the water it moves toward the basic side, and we call it "hard" water. That results in all the white deposits on cars after washing them if the water is from underground supplies. Water softeners remove those minerals so they do not build up inside pipes or the tubing of things like a coffee maker.
View past Ask Mr. Pest Control questions.
How much effect does the pH of the mixing water have on the efficacy of Bifen 7.9 and what is the ideal water pH for mixing with Bifen 7.9?
ANSWER:
It is probably a good idea to know in general what the quality is of the water used to dilute pesticide concentrates, and for that matter even the pH of the soils and other surfaces you apply the sprays to. Water that is high in alkalinity (a high pH) is more likely to affect chemical molecules than one that is slightly on the acid side (lower in pH). If my basic chemistry knowledge is still correct the scale of pH runs from 0 to 14, with 0 being extraordinarily acidic and 14 being terribly alkaline (also called "basic") and with 7 right in the middle as neutral. Plain, clean water is supposed to be right around 7.0, but when minerals are in the water it moves toward the basic side, and we call it "hard" water. That results in all the white deposits on cars after washing them if the water is from underground supplies. Water softeners remove those minerals so they do not build up inside pipes or the tubing of things like a coffee maker.
What is preferred is a pH just slightly on the acid side, but each jump of one number is a 10-fold change in the acidity or alkalinity, so water with a pH of 9 would be 10 times more alkaline than water with pH 8. A simple swimming pool test kit should be sufficient for testing the waters you use in your tanks.
The effect of pH, and in particular alkalinity, was much more of a concern with our old Organophosphates and Carbamates than it is with the current Synthetic Pyrethroids. Whatever the chemical reason for it, the OP and Carbamate molecules were really affected by alkalinity and tended to break apart. One vendor rep for a carbaryl product told us once that adjusting the pH down from alkaline to acidic could extend the life of the product on foliage from 1 day to nearly 60 days. Now, that could be pretty optimistic, but it at least demonstrates the huge benefit of using slightly acidic water for those classes of pesticides. The pyrethroids do not seem to be nearly as susceptible to alkalinity and it really has not been an issue pushed by the manufacturers of these products, but I suspect it would still pay to test the pH and keep things close to neutral at least.
Adjusting the pH is simple, and Univar ES sells a number of "buffering agents" that will bring the pH down, as well as some other general surfactants that include a buffering agent. These can be added to the tank when you mix the products for use. We also know that some surfaces may have a high pH, such as concrete or stucco or sheetrock, although paints may cover these to reduce the alkalinity of the actual surface you treat. But, unfinished surfaces might have an effect to more quickly break apart pesticide molecules and reduce the residual effect.
View past Ask Mr. Pest Control questions.
