1 Wait two to four months to re-seed the lawn after using a pre-emergent herbicide. 2  Use a pre-emergent herbicide during late winter or during early spring of the next year to prevent any crabgrass seeds left behind from developing at the next opportunity.f the crabgrass seeds have already sprouted and crabgrass has appeared in your grass, the pre-emergent herbicide will do no good. However, you still have an option. Post-emergent herbicide products control crabgrass after it has already germinated. Post-emergent herbicides work by killing the crabgrass plants.