Answer: Crabgrass is an annual weed so it will die down when the weather gets cold. At this point you might want to try raking it out or hand pulling. Next spring use the pre-emergent, reapplying in 30 days. That should keep the crabgrass under control. Crabgrass starts germinating when soil temperatures are 50 to 55 degrees F for ten or more days and germination can take place over a 6 week period. Pre-emergence herbicides provide excellent weed control for crabgrass but they last only about 30 days. The compound prevents the weed seed from germinating, but it won't kill the newly sprouted seedlings. Late April to early May is an ideal time to apply pre-emergence control. A second application might have keep your lawn a little more crabgrass free. Best wishes with your lawn.
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