I have a question about time and amount of application of Surflan. I live in Powhatan, Virginia (near Richmond) – I overseeded my lawn in September 2010 – my lawn is fescue. When would be the best time to apply Surflan to prevent crab grass in the lawn and at what rate?
SURFLAN prevents all seeds from growing so it was important that you waited till after you overseeded in September. In general it's good to wait at least 3 weeks following the over seeding to insure the seedlings get a chance to root with out extra stress. And yes, Surflan in theory shouldn't affect them, but because they're young and vulnerable, waiting a little is always the smart thing to do.
I too use Surflan and generally do a treatment after we over seed. Coincidentally we over seed in September like you. That means my first treatment of Surflan is in October and then again in February. Since it sounds like you haven't applied any yet, I suggest you do so ASAP to help minimize unwanted weed growth this spring. And I suggest you do a followup application this spring, at the end of April, just to be sure you've got everything covered.
Now if you apply the Surflan at the rate of 1 oz per gallon per thousand sq/ft, you'll get 2-4 months of protection. This would be the "low" rate. And based on the fact that you just seeded, this is suggested. Once you get to spring and see how this rate does, you'll be able to determine if you need a stronger dose for future applications. Generally speaking everyone's yard can be different and there is no need to use the high rate immediately. That being said, doing more applications using less product is suggested when possible and how I like to use it.
Here are direct links to the information and products listed above:
Surflan Label: www.bugspray.net/labels/surflan_label.pdf
Weed Control Article: http://www.lawn-weeds.com/weed-control