Between Christmas and the New Year, mix up the 10% vinegar, orange oil and soap herbicide and spray it over the area where you have any type of weed growing. It will not harm the dormant grasses.
Vinegar Herbicide Recipe:
http://www.dirtdoctor.com/view_question.php?id=134
Weeds are an indicator of imbalances in the soil. There are always weed seeds of all kinds laying dormant, just waiting for the right conditions to come along for them to germinate. (The reason I believe people sometimes have trouble with successfully using corn gluten meal as an pre-emergent). Certain weeds will grow as a result of certain conditions. The links below will take you to a few great books on this subject.
Check out:
http://www.acresusa.com/books/closeup.a ... =10&pcid=2
http://www.acresusa.com/books/closeup.a ... =10&pcid=2
http://www.acresusa.com/books/closeup.a ... =10&pcid=2