Answer: I'm afraid that if you feed this late in the season you could damage your lawn. Crabgrass is a warm season grass and will die out this winter. To keep the seeds from germinating next spring, use a pre-emergent herbicide. If it were my lawn, I'd lift the grass at the seams and pull the weeds, then replace the sod and press it down so it makes better root/soil contact. Once the grass knits together, weeds should not pop up at the seams. Getting the roots of the weeds will get rid of them. In the spring you can apply a pre-emergent herbicide which will keep weeds from sprouting.
Best wishes with your lawn!
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