Answer: Crabgrass pre emergents will keep grass seeds from germinating but if the crabgrass has already sprouted, pre emergence products will not affect the plants. You might try a post emergent crabgrass controller on your lawn now, then wait 2-3 weeks and overseed your lawn. Or, wait until this fall to overseed and you won't have to time your crabgrass control applications with such accuracy. Best wishes with your lawn.
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