In preparation for fall seeding, have you sprayed your lawn for weeds, but they're still there?
The problem could be with the type of herbicide you are using. If you are using a broadleaf herbicide such as Triplet or 4 Speed XT and your weeds are still there, chances are broadleaves are not your target.
Especially with the weather in the Mid-Atlantic this year, tougher weeds such as crabgrass, goosegrass and nutsedge are major problems in lawns.
These weeds require different herbicides to control them.
If you need to control crabgrass or goosegrass in your lawn, you'll need a herbicide labelled for grassy weeds - such as Quinclorac 75 DF.
For nutsedge control - you would need a herbicide specifically designed to eradicate nutsedge - such as Pro Sedge. 
Knowing the types of weeds you are trying to control in your lawn is important and can save you time and money when it comes to controlling them.
One thing I have learned this year: Japanese Stilt Grass is a MAJOR problem for landscapers and homeowners in this Maryland/DC area.
So what is Japanese Stilt Grass and did it come from Japan?
YES - Stilt grass originates from Japan. It was used as a packing material for porcelain in the 1900's and it is believed that seeds in the packing material were unintentionally introduced to North America.
Why is it a problem here?
Japanese stilt grass spreads rapidly, especially in areas that have been disturbed. Unlike most grasses, it can grow prolifically in the shade and densely cover wooded floors, thereby preventing the growth of other plants including young trees and shrubs. To make matters even worse, our animals don't seem to have a taste for it.
Control Options:
Where and when possible, manual removal should be the primary method of control. For larger infestations, chemical control may be possible.
You can use a non-selective herbicide such as Razor Pro (glyphosate) or if you would like to selectively eradicate the stilt grass - you can use Acclaim Extra (fenoxaprop) - Acclaim will also help you knock out some of the crabgrass in your lawn as well.
I know, I know - your lawn doesn't have crabgrass (wink, wink)
Consult labels for specific use rates and controls.
In preparation for fall seeding, have you sprayed your lawn for weeds, but they're still there? 
