Wild violets (Viola species) include several cool-season annuals and perennials with low-growing habits (2" - 5"). These species are very shade tolerant and prefer lawns located on moist, fertile soils. Violets tend to be most visible during cool weather of spring and fall. Leaves of the common violet are oval to kidney-shaped with a heart-shaped base. Flowers may be white, blue, purple, or yellow. All violets reproduce by seed, and perennial violets also spread by creeping roots and rhizomes.
To keep ground ivy and violets from invading lawns, maintain a thick lawn by proper lawn care practices. Unfortunately, grasses in shade areas are not as competitive against weeds as those in full sun. In some shade situations, violets may be desirable in some woodland areas.
One control option is to dig out existing violets. Pull up all the roots and stems or the plant will grow back.
Although control is difficult, existing violets can be treated with post emergence broadleaf herbicides in the period from mid spring to early summer and/or mid to late fall. Regardless of the time, make sure the weeds are actively growing.
Another herbicide is chlorsulfuron. It has been on the market for many years primarily for the control of tall fescue in Kentucky bluegrass turf. However, it is labeled for the control of wild violets, chickweed, and purslane and several other weeds. Check label for specifics as this product is not to be used on tall fescue or ryegrass, and there are other restrictions.