Influence of pH on pesticides. Most crop protection agents work best in an acidic to slightly acidic spray mixture (pH 4-6). Many mediums are unstable from a pH greater than 7, because they are degraded by alkaline hydrolysis (saponification) (for example, phenmedipham, many pyrethroids, dimethoate, cap tan). The loss of effect is irreversible and, as soon as the pesticide is mixed with the water, it begins and lasts until the active ingredient has dried on the target surface. Depending on the active ingredient and pH, 50% of the active substance may be degraded after just a few minutes. In general, insecticides are more susceptible to alkaline hydrolysis than fungicides and herbicides.
Also the water treatment plays a role The solubility of many pesticides and foliar fertilizers decreases with decreasing temperature. With warm water, the time required to dissolve a substance, especially saline components, is significantly shorter than with cold water.