Check the label and make sure that wild violets are listed on the label. The label is the law and all you can do is follow label directions and timing for control. Wild violets are difficult to control. Another option is to look for an herbicide with the active ingredient triclopyr and follow directions and timing for control. 

Violets thrive in moist, shady sites, but tolerates drought once established; They also thrive if mowing the lawn too short. They are common in thinning lawns that are in poor condition. Maintain a healthy, dense turf that can compete and prevent weed establishment. Test your soil for pH, liming, and nutrient deficiencies and overseed in the fall to thicken up the turf. https://extension.umd.edu/resource/lawn-renovation-and-overseeding

Also, in general, wild violets are native and they do have wildlife value. They are the larval food source for fritillary butterflies. https://extension.umd.edu/resource/wild-violet

Marian

You are welcome.

Marian