Our Prosquito is very effective, but it takes a day or two to take full effect. After that, it lasts about a month until our next treatment. Large rains may cause a large mosquito hatch that may overwhelm the application for a day before control returns. You will never have zero mosquitos. But if you have 20 “slaps” per hour before our treatment, you should easily get down below 1 “slap” per hour.