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Lawns in shade areas are rarely very vigorous or dense and thus may be prone to weed invasion. Two of the more common broadleaf weeds invading shady lawns are ground ivy and violets. Both are difficult to control.
Ground ivy (Glechoma hederaceae), also called creeping Charlie, is a common lawn weed problem. Shady lawns with poorly drained fertile soil are typical sites for ground ivy to develop into a major problem. This plant may form extensive patches as it creeps along the soil and moves into sunny areas. The stems are square and the leaves are arranged opposite of each other along stems. The leaves are round to somewhat kidney shaped with rounded, toothed margins. Crushed leaves have a minty odor. Ground ivy has small funnel-shaped purplish-blue flowers appearing from April to June.
Violets (Viola species) include several cool-season annuals and perennials that are low-growing plants. 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. Reduce shade by pruning (see Managing Lawns in Shade Areas). In some shade situations, the ground ivy and violets actually functions quite well as a groundcover and maybe desirable in some woodland areas.
One control option is to dig out existing ground ivy or violets. Pull up all the roots and stems or the plant will grow back. This option works well if ground ivy has gotten a foot hold in a flower or shrub bed, and you can prevent the spread into the lawn. If you are starting a lawn using organics, it is important to rid the lawn area of creeping Charlie and violets before you establish the lawn.
Although control is difficult, existing ground ivy and violets can be treated with postemergence 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. For ground ivy, herbicides should contain dicamba. Three-way broadleaf herbicide combinations (one product containing all three herbicides) that include 2,4-D (2,4-dichlorophenoxyacetic acid); mecoprop or MCPP (2-(2-methyl-4-chlorophenoxy) propionic acid); and dicamba (3,6-dichloro-o-anisic acid) may provide the best control. Several of these three-way herbicides are available.
Check product labels for these active ingredients. Read and follow all label directions. Herbicides containing 2,4-DP or triclopyr may also be effective. For violets, broadleaf herbicides containing triclopyr are suggested. Professional turfgrass specialists available for hire may use products containing 2,4-DP or triclopyr. Refer to the Illinois Commercial Landscape & Turfgrass Pest Management Handbook for details on these herbicides.