Even a lawn that is largely crabgrass free should be treated with pre-emergent, I believe, as crabgrass seeds are easily transported to a lawn in autumn by wind, rain, birds, pets and so on.Too, crabgrass seeds can lay dormant for years, waiting for prime conditions to sprout.ven a lawn that is largely crabgrass free should be treated with pre-emergent, I believe, as crabgrass seeds are easily transported to a lawn in autumn by wind, rain, birds, pets and so on.