Remember that crabgrass is the number one weed in every yard and if it is not killed at the root, it can easily become a never-ending problem. By applying crabgrass prevention at the start of the season, you have to kill the weed at the surface, thereby preventing it from germinating and populating. When paired with fertilizer, you are getting the best of the two worlds, killing weed and feeding your yard.
Two factors that play a role in how well your weed killer performs and how it lasts is precipitation and heat. If there is more rain and/or heat than usual, then it’s going to reduce the amount of time you weed killer is affective.