If it rains heavily sometime after applying as described, can it be washed away? As in a day or more after correct application.

Hi - Yes, rains can wash the Sevin granules off the treatment area which is why we recommend a controlled watering. Applying this product in calm weather when rain is not predicted for the next 24 hours will help to ensure that wind or rain does not blow or wash pesticide off the treatment area. Sweeping any product that lands on a driveway, sidewalk, or street, back onto the treated area of the lawn or garden will help to prevent run off to water bodies or drainage systems. Thank you.