A spreader-sticker should be used in fruit tree sprays to improve the distribution and retention of fungicides and insecticides on fruit and leaves. However, even with a spreader-sticker, a rain can reduce the length of time the materials are effective. Less than one inch of rain since the last spray will not significantly affect residues. One to two inches of rain will reduce the residue by one half. Reduce the number of days until the next spray by one half. More than two inches of rain since the last spray will remove most of the spray residue. Re-spray as soon as possible. Details on when and what to spray are available in the K-State Research and Extension publication, “Fruit Pest Control for Home Gardens” at http://www.ksre.ksu.edu/
Good article. Also note on the spray container instructions – the best time to apply to not affect pollinators (like honey bees) adversely. Timing of fruit tree insecticide spraying to occur before or after the work by the pollinators is a good rule of thumb and noted on most spray specifications.