I would nail the crabgrass with Round Up using a sprayer, give it about 7-10 days for the CG to die and wither away, then overseed.

Just went through the exact same thing.

thanks for the help nc lawn nut. I will probably give that a try. What did you do to remove the dead crab grass roots and mess before seeding ? thanks

I set my mower to the lowest setting and scalped the lawn and used my bagger.

fangbuster: although I live in the south and have bermudagrass, I'm in a similar situation.

I have TruGreen take care of my lawn so they have definitely used pre-emergent, post-emergent (several times), whatever and lately I've been getting a lot of crabgrass, so I experimented using the Weed-B-Gone and spraying it directly onto some of the crabgrass.
Well, it died, and today I went to remove the dead crabgrass and ended up with a huge divot in my pretty lawn :(

I don't know if it was necessary to remove the root "balls" but they were everywhere... don't want to take any chances. I removed the roots by using a weed hound and by just getting hold of the root bundles and yanking them out by hand. Then of course I filled my hole with topsoil.

TruGreen said that the crabgrass will eventually die on it's own as fall comes around, but I just wonder about those roots!

Thanks hsvara. I don't think those root " balls" will go away soon. Was thinking of picking up a "weed Hound" do you like it?

Depending on how you reseed/overseed, the roots of the crabgrass may well get pulled out or chopped up. I have had decent success with cutting the post-treatment lawn as low as possible and then running a slit seeder over it to overseed. I believe the crabgrass (and roots) was largely eliminated by the combination of stress (from scalping), herbicide, and the blades of the slit seeder. I suspect core aerating would have a similar impact on the crabgrass roots.

Of course the cg seeds are still in the soil waiting for Spring 09...

I do have a Weed Hound and like it very much, but primarly use it on dandelions.

I wouldn't worry about the crabgrass roots. Just hit the crab grass with either weed B gone or round up. If you do use round up...be carefull, it will kill anything it gets on where weed b gone is more selective.

Either way, you can scalp the lawn and seed in a couple weeks. Leave the dead crab grass alone. If you use KBG you'll get germination all around the crab grass. Over the next couple of months it will rot away slowly and the new KBG will spread and cover over what is left of the CG and roots. By next summer, you'll never know it was there.