I use a systemic insecticide by Bayer, avail in Lowes, Home Depot, Wal Mart etc.

Fire ants make mounds and not holes. The mounds start out small and become larger as the colony population increases. These mounds look rather innocent until you disturb them, and ALL of the ants boil out of the mound all at once. Again, there is never a discernible hole. I never worry about ants in my yard and garden, other than fire ants. Fire ants can be a problem for humans, pets, bird nests, beneficial insect eggs and larvae, and such.

What do they look like? What color are they, and do they grow from leaves that all come from the ground, like dandilion leaves do, or do they grow up along a stem? Are the leaves heart shaped? I'm curious, because I didn't think sweet or fragrant violets were winter hardy that far North. As far as eliminating violets from a lawn, I did spot some threads on that posted long ago--somewhere on thread pages 11 through 13, I think. We have quite a few little purple violets in our lawn that are typical to our area, and I would, personally, never give them up--they look lovely in early spring, when the grass is at its worst. After my husband mows the lawn, you can hardly see where they are. You might try reseeding your lawn a bit with some grass seed especially for shade, if it has become a more shaded area over time. Violets like partial shade, and possibly are competing with a variety of grass that can't compete. For more desperate measures, the old threads might be helpful to you. ;o)

I see this is an old post but new people may have these same questions and this past fall i did the same thing that g6342856 did. I had a weedy area about 4000 sq feet on side of house that had agressive weeds and only a few small patches of healthy grass .So i first mowed to lowest possible setting then round up for a month like morpheuspa said. Then water the dirt each week to see any areas you missed then repeat round up again. After a months time either level the area or rototill .If area is level just rough up the existing top soil and sow the seed. Before you do this incorporate some starter fertilizer into the soil that prevents weeds and does not interfere with new seedlings. Then your good. I recently filmed a two month renovation i did in August and i used titan rx turf type tall fescue with good results and im now weed free you can see video below. It took some hard work but well worth the wait