Malathion is hard to find, though it once was the most common fruit pest control insecticide. Malathion will also break down if the pH of the water is high, but not as easily as captan. It is stable at a pH between 5 and 7. Lambdacyhalothrin is found in Bonide Fruit Tree and Plant Guard and is also stable between a pH of 5 to 7.
Not all pesticides are susceptible to alkaline hydrolysis. Check out this resource, distributed by Cornell University, for more information about pesticide sensitivity to alkaline hydrolysis.
If your water pH is too high, food grade citric acid can help. With a pH of 8, add 2 ounces of citric acid per 100 gallons of water (1 ¼ teaspoons per 10 gallons) to bring the pH down to about 5.5. Contact your local Extension office for instructions on how to test the pH level of your water. Here is a map from our K-State Research and Extension website to help you locate your local county Extension office. (Cynthia Domenghini)