How can you control Wild Violets in a lawn without killing the turf?
Fall is the best time of year to control the wild violets. It's a perennial weed with a long tap root on it. Use a broadleaf killer that contains 2,4-D or Dicamba, and it will selectively kill the violets without damaging the grass. Another great wild violet herbicide is called Drive (quinclorac). Quinclorac is also sold in other lawn weed control products, under differing names.
Because violets have such a waxy leaf surface, adding a spreader-sticker product to the herbicide mixture will result in better adhesion of the herbicide to the leaf surfaces, resulting in better control. Ask for a spreader-sticker product at your local garden center.
One treatment won't do it. They will have to make multiple treatments. Spring or summer applications only burn back the leaf tissue back, and the plants will grow back. Herbicides appliced in fall translocate down into the tap root better and give better success with control.