I already put down broad leaf liquid weed killer a month ago and its
working well on my lawn, there are hardly any weeds. But there are a
couple of crab grass patches on the edge, and I am worried they will
spread inland and cause havoc.

Any tips here? Is there something specifically and only for crab grass?
Should I just kill it off and reseed it in the fall?

Cheers for any tips,

Dean