From everything I know, you need to put down pre-emergent about the time Forsythia are in flower in late winter/early spring.

I have lots of crabgrass in some areas and am removing it before it flowers and seeds. If you can do that, it helps the regular grass to grow instead of being crowded out.

I think there is Weed B Gon with crabgrass control for a hose-end sprayer. I used Weed B Gon for Oxalis and it worked but I need to repeat the application in a few spots.
If the area has not had sufficient rain, the chemicals won't work. The ground moisture must be present in order for it to be effective.

September is the best time to sow grass and that way you can get the lawn growing well prior to next spring's treatment.

The single most effective method of controlling crabgrass is to make the lawn grow in good and thick, a good, healthy soil is a start.
A good stand of crabgrass now is very difficult to control, without killing even the grass you want to grow, because anything that will crabgrass will alos kill the desireable grasses. Once the crabgrass is up and growing a pre emergent will not be of any help, that needs to be put down 6 to 8 weeks before the seeds will be germinating which they do when the soil temperature reaches 55 to 60 degrees F for several days. Depending on where you are that could be about when the Forsythia does blossom, or maybe earlier, or maybe later. I don't see crabgrass growing around here until July, almost 12 weeks after the Forsythia blossoms.
Are you growing cool or warm season grasses? For those of us in cool season grass areas the best time to seed is the end of August to the end of September. Elsewhere may be different. Zone 7A tells us which plants will survive a normal winter in your area but not much else.

Thanks for the responses.

"Are you growing cool or warm season grasses?"
I have what was in the ground when I got here and I just bought a bag of Pennington Seed Smart Seed Landscapers Mix Tall Fescue/Bluegrass which I think is supposed to match what Maryland needs.

It sounds like I should put grass seed down September/October and then pre emergent 6-8 weeks before several days of 55-60 highs.

Would it be ok if I pulled the existing crabgrass just to get it out of the way before I put seed down in the next month or so? I know it won't really get rid of the crabgrass since it's dropped it's seeds already but I just want to expose the dirt to the grass seed. The crab grass is pretty thick in many spots.

Is Scotts Turf Builder Crabgrass Preventer Fertilizer decent? I'm always nervous about putting herbicides or fertilizers down since I've over done it in the past and killed the grass but this crabgrass issue is just too much.

Since I won't use any synthetic fertilzer or poison because of the harm they do to the environment I cannot state whether any of the Scotts products are decent.
My crabgrass control method is to grow a good, healthy stand of turf grass and pull out any crabgrass, or other "weeds" that might grow in my lawn where tjhey get mulch mowed back into the turf so the nutrients they removed from the soil will go back.
Your states agriculture school, either of your state universities, will have Coopertive Extension Service offices that can supply you with information about which turf grass is best and many other bits of information that can be helpful.

1) Which one? Scotts Turf Builder Crabgrass Preventer Fertilizer gets good reviews but it doesn't seem to be available locally. Is there a better brand? I'm real concerned about over doing it with a liquid and thought a powder/pellet would be easiest to control, like Scotts or Preen.

Now is the time to use pre-emergent to control winter annual weeds, not summer annuals like crabgrass. But you can't do that and sow new seed that establishes before winter. I don't think there is any brand that is superior. You definitely should use a granular substance though. Corn gluten meal is another option as well.

2) Can I do a fall crabgrass preventer application or does it have to be in the spring?

Spring. Crabgrass doesn't germinate in the fall and the protection will be long gone by Spring when the seeds germinate. Concentrate on planting a new lawn now instead.

3) Would it help for me to pull up the current crabgrass before putting down the preventer?

Yes, pull as much as you can (including roots) so the new grass has space to germinate.

5) I have an unopened bag of Pennington Seed Smart Seed Landscapers Mix Tall Fescue/Bluegrass. I can return it if it's bad for 7A or with a crabgrass infested lawn (or bad in general).

I live in 7A (a transition zone as far as turfgrass goes) and the general recommendation from Extension services is a turf type tall fescue/bluegrass combination. You can use warm season grasses, but zoysia is very expensive as sod and takes forever to fill in from plugs. Bermuda (I think) can be grown from seed -- but generally the dormant period leaves it looking straw colored for about half the year, which is generally frowned upon. It is just a touch too cold for many of the other warm season grasses.

6) Any other tips?

Yes. Buy a Ph tester. The Ph needs to be neutral (7.0) to slightly acid (6.0) in order to absorb nutrients properly. If the area is under 6.0, you need to add the appropriate amount of fast-acting lime to the soil. Make sure the area gets at least 6 hours of sunlight or you will struggle with keeping the grass thick and dense enough to keep weeds at bay. Also, be sure your soil isn't compacted because that impedes the rooting of the turfgrass. You can buy a step-on aerator at Home Depot or similar places for about $20 that will help loosen the soil by removing small plugs of soil. After aerating, you prepare the seedbed by mowing as low as possible (you can do this before aerating but after pulling all crabgrass you can), then top dress the surface with about 1/2 inch of compost. You sow the seed onto this and maybe put on an additional 1/8 inch of compost to cover the seed. Walk on it so the seed makes good contact with the soil. You can also add starter fertilizer at this time according to package directions. Do not add regular lawn fertilizer. After that, the key is keeping the seedbed moist. Do not saturate it with long sprinkler runs -- just keep it constantly moist. Just take the hose and moisten everything a few times a day.

The alternative is sod -- which has completely different guidelines but is affordable for small areas and less prone to failure because you are dealing with established grass and not trying to nurse along babies from seed. The key there is keeping it drenched for several weeks until the roots establish into the soil. You would still aerate and top-dress with compost, though.

For sod, you would actually "bottom-dress" meaning put compost down under the sod before it goes down.

Aeration also counters compaction, which can occur on lawns with lots of foot traffic. The micro-organisms in the compost will help to aerate the soil as well. I would not chemically kill the crabgrass and then seed turfgrass because the weed killer may impede the germination of the seed.

Thanks again for all the great feedback! Here's my plan:

1) buy a Luster Leaf 1612 Rapitest pH Soil Tester and Earthway 2750 Hand-Operated Bag Spreader/Seeder.

2) carefully pull up the crabgrass with as much root in mid-September, hopefully on nice days!

3) prep the bad spots by loosening up the soil. It isn't a big yard and the bad spots add up to maybe 100-150 sq ft so I think I'll just turn it over some with a pick ax and shovel.

4) around the end of September mow on the lowest setting

5) add Scotts Turf Builder Seeding Soil to the spots that had lots of crabgrass, spread out cheaper dirt elsewhere

6) seed everywhere with over-seeding in the bad spots using the Pennington Seed Smart Seed Landscapers Mix Tall Fescue/Bluegrass I already have

7) add some more seeding soil on the the bad spots

8) try to water as much as possible! (probably every other day)

9) hopefully see lots of sprouts

10) winter passes

11) Put Scotts Turf Builder Crabgrass Preventer Fertilizer down 6-8 weeks before the first average high of 55 which should be around 1/19/2013 - 2/02/2013

12) watch for crabgrass sprouts like a hawk and carefully pull any I see roots and all (I hope to see none!)

13) mow on high to let the new and old grass block out weeds

14) Enjoy great lawn!

A few things:

Crabgrass preventer is applied when the soil temperature is 55 degrees, not the air temp. Best way to do it is test your soil temp 4 inches down with something like a meat thermometer. When it is 55 down there, then you apply the crabgrass preventer. This is usually late March to mid-April around here.

Also, I would do the reseeding, etc. now and not at the end of September. You want the grass to be well established before frost. The more time you can give it, the better. We are out of the danger zone 90+ temps here on the East Coast. Again, not sure where you are, but the time to reseed is as soon as the oppressive heat of summer has abated and highs are in the 80s, lows in the 60s -- usually mid- to late August. You can wait until late September, but your grass has a better chance to make it through winter if you seed now.

You want to water a little bit, twice a day. Watering every other day likely won't keep the soil moist enough for germination in a full sun area. You literally just dampen the soil, but do it at least twice a day. Once the grass is established, you water deeply (meaning at least one hour with a sprinkler) once a week assuming there are no soaking rains during that week and only during the growing season (spring/summer/fall).

Compost is superior to any so-called "seeding soil." Seeding soil contains peat moss which has zero nutrients, steals nitrogen from the surrounding soil, and impedes drainage of clay soils. Compost improves your soil structure and provides nutrients for your growing grass.

If your soil is compacted (likely it is if you have a ton of shallow-rooting crabgrass), you will have limited success if you do not aerate and remove thatch buildup with a heavy rake.

Soils become compacted because there is little to nothing to seperate the mineral soil particles to allow air into the soil mix. Organic matter can do that by seperating those soil particles in clay soils. Punching holes in soils is merely a short term solution that really needs a long term fix and adding adequate levels of organic matter in soils is that long term fix.
A good, healthy soil will not have much thatch buildup and thatch of 1/2 inch can be helpful in creating a good, healthy soil which will have a good active Soil Food Web that will keep that thatch buildup under control. Compost is one form of organic matter as would be the grass clippings, leaves from deciduous trees and any other type of vegetative waste.

^ The above is absolutely true, but a poor soil profile is not the sole cause of compaction. Even organically healthy soils can be compacted by the weight of riding lawn mowers, pets, or people. Also, heavy clay soils like we have in the Mid-Atlantic tend to become compacted naturally, especially in water-logged or developed areas where natural soil aeration processes can no longer take place. Core aeration is considered a method of periodically alleviating compaction in soils. Some soils may never need it, some may need it yearly depending on conditions and land use. Aeration with a top dressing of compost that fills the plug holes ensures that the organically rich material penetrates the soil profile and starts to allow for better air penetration into the root zone.

OP, you may want to cross-post this in the Lawn forum because there are many experts there that can give you other perspectives as well.

Here is a link that might be useful: More info