Eliminate ANY places in your grow where there is standing water or soggy dirt. Check the drip trays under your plants. If you are using pots with built-in catch saucers, REMOVE the saucer. Wash all drip trays thoroughly with hot soapy water before returning to grow room, and wipe down the bottoms of your pots. This is where they breed... eliminate the possibility of reproduction, and you eliminate the problem.