I know some people reapply every time it rains and for that week or two when the beetles are worst I did diligently reapply (I also did earlier in the spring when the cherry trees got attacked by some type of black aphid which was destroying the new growth). I think I only had to do it twice for the beetle invasion, though. I learned you can put the mixture in a hose sprayer and set the dial, allowing you to do a lot of trees very quickly.