This product is a pre-emergent selective herbicide. And, it's going to control one of the toughest control lawn weeds around. Which is crabgrass? Which is actually a grass that is going to be controlled in your grass lawn? And, that's a real trick when it comes to herbicides. It says it's a grass stopper. It also says, it's a pre-emerge grass preventer. And, what that means is that you're not going to have grass growing out there. You're not going to have crabgrass when you apply this product. You're going to be killing the weed seeds, the crabgrass seeds and other weeds. Because, it controls broadleaf weeds also that are lying in the ground just waiting for conditions to get right. So, if you're going to apply this this spring to control crabgrass and other broadleaf weeds that are going to come up. You want to do it several weeks or even a month before you expect to see the weeds. And, you're going to have to have a history of the lawn to know where these weeds are. So, that you can apply the prevention to the area that's most likely to have the weeds. It's something that needs to be done as a prevention, not as a cure. Because, this will not kill growing crabgrass and the other weeds that are on the label.