One of the most difficult weeds to control in lawns is the wild violet. Even combination products that contain 2,4-D, MCPP and Dicamba such as Trimec, Weed-Out and most formulations of Weed-B-Gon do not do a good job. Products with triclopyr give much better control though more than one treatment will likely be needed. A couple of products that contain triclopyr on the homeowner side are Turflon Ester and Weed-B-Gon Chickweed, Clover & Oxalis. (Note: There are several formulations of Weed-B-Gon but only Weed-B-Gon Chickweed, Clover & Oxalis contains triclopyr.)
Both products listed above are labeled for tall fescue and Kentucky bluegrass. Do not use products containing triclopyr on bermudagrass as severe injury will occur. Weed-B-Gon Chickweed Clover & Oxalis is labeled for buffalograss and zoysia (Turflon Ester is not) but lawns will likely show some temporary browning after application.
Spray only on calm days and when temperatures are below 90 degrees to avoid damage to nearby plants. (Ward Upham)