Everything that I read indicates that the pre-emergents build a "barrier" to seed germination. I have no idea whether it's a real barrier or a convenient mental picture from the vendors, but I did see a posting (on this forum I think) last year about spots where car tires went off the driveway and mushed up the soil actually having crabgrass where the soil was disturbed - but nowhere else. I may be falling prey to vendor marketing here, but I know that you're not supposed to core-aerate the lawn after you have put down pre-emergent. I have a feeling that someone who's a pro may shoot me down on this one. If you can't plug, I would imagine that you shouldn't top-dress.

Thanks Andy.

My first inclination is that if I top dress, I'm going to have to wait a few weeks before I put down pre-emergent crabgrass control.

Holy cow! How much topdressing did you use? Usually crabgrass needs direct sunlight to germinate. And usually when you topdress at 1/4 inch or so, the grass is tall enough to prevent crabgrass seed from germinating.

How high do you mow? and how often do you water? These are critical issues with crabgrass germination and continued cultivation.

When you see grass growing in your mulch, hoe it out.