That's a big project, you're probably facing multiple apps of herbicide, multiple drops of seed, etc. Timing is important but what is your overall time frame?

My timeline is pretty flexible. I'd love to hear your advice regarding the timing of herbicide applications and seed drops. I forgot to mention that I plan to aerate first, given our hard clay soil, and read that I should wait four weeks after aerating to seed.

It's problematic. You have to wait 60 days from germination to pre-emergent, and so if you won't be able to apply pre-emergent until mid May. You can hold the fort with Tenacity every 3 weeks, but it doesn't control everything - Bermuda being the biggest one that it doesn't control. Also, with shallow roots you will have to water very often, which opens the door to major fungus issues.

It sounds like waiting till fall is really the best thing to do.

So are pre emergents used in the fall, or will a broadleaf weed killer like Weed-be-Gone, applied a bit before dropping grass seed, be sufficient?

I'm seeing a trend on the forums and the Carolinas are right in the middle of the issue. With the Earth getting warmer, the transition zone, where either warm season or cold season grasses can be grown, is moving north. I think you will be fighting your lawn from now on if you continue with northern types of grass. If you lived in North Carolina I would say the same thing, so South Carolina is definitely moving into the warm season grass zone. The fescue you're looking at needs to be reseeded every fall to keep it dense, whereas the southern grasses tend to spread and form a carpet that does not need to be reseeded - ever. Would you consider changing to a hybrid bermuda like TIF 419, St Augustine (good for shady areas), or zoysia. The hybrid bermuda would be expensive unless you sprigged it. The St Augustine could be expensive unless you are patient. Zoysia really depends on what you want and how fast.

Is the area going to be used for sports activities?

Do you have a watering system for the area?

Pre-emergents block (almost) all seed from germinating, including the grass seed. You can apply it in the fall for winter annuals, but you have to wait 60 days from germination because they are root inhibitors and will injure the new grass.

Most broadleaf herbicides have a waiting period from application to seeding. As long as you respect that time period you should be ok. Typically, it is not broadleaf weeds that cause most issues in the summer but grassy weeds - crabgrass, bermuda etc.

My suggestion: apply prodiamine at 5 month rate March 1st to keep summer weeds under control. This will take care of 99% of germinating weeds. Late August, Round-up trouble areas. Wait a few days and begin to water daily for a week to sprout more weeds. Round-Up again. Reseed mid-September.

Thanks for the responses.

dchall, that's an interesting point about the transition zone moving north. Luckily we still see a lot of fescue lawns around here that seem to do pretty well. I'm glad about that because I'm just not a fan of the look of the warm weather grasses during the winter and spring. We do have a sprinkler system, but we've actually never used it since we moved in a couple years ago, so I'll have to check that out.

j4c11, I'm concerned that if I kill all the weeds in march, we will spend the summer with a bare muddy lawn, which would be real pain with the dog and kids. Is it possible to spray in august instead?

You can skip the spring pre-emergent if you'd like and just mow the weeds through summer. My concern is with Bermuda seed, but it's probably pretty bad already. Then Round-Up in August.