One thing I know for certain is that if you want to grow new grass from seed, you cannot put down any herbicide other than one specifically designed for that purpose. Almost any other crab grass, clover, weed, etc. herbicide will prevent new grass from growing. Also, starter fertilizers (i.e., fertilizer/herbicide designed for seeding) is not nearly as good as preventing crab grass and the like as the regular stuff.
If you have discrete, confined areas you want to seed, you can cover them with a garden fabric or other material before you apply a herbicide in order to try to prevent the herbicide from falling on the bare patch you are seeding. Heck, even sheets of cardboard would probably work for that purpose, as I don't think the herbicide will migrate all that much.
Of course seeding is always better in the Fall. But if you are like me, you always forget about that until right around this time of the year when you are looking to put down fertilizer/herbicide.
