Lurking in the shadows
Both cultural and chemical maintenance is needed to rid turfgrasses of ground ivy and violets.
One of the challenges in turf care is maintaining quality turf in areas of moderate to heavy shade. Turfgrasses in these sites become thin and weakened, resulting in low-quality turf. In addition, the shade environment often hosts thriving, aggressive broadleaf weeds that readily invade thinning turf. To the frustration of the individual managing shaded turf, the broadleaf species usually prevail. Ground ivy and violets are two species that typically infest these shaded turfs and controlling them involves both cultural and chemical options.
Lawn care professionals typically try to handle the problem by applying a broadleaf herbicide. Certainly, there are some broadleaf herbicides that can provide control, but the weeds often return in a short time. As with many weed problems, the long-term solution is an integrated combination of cultural and chemical controls.
To solve these problems, you must understand the invading weeds and the site factors that favor them. Also, you must understand which herbicides the weeds are most susceptible to. Further, you may have to make modifications to the environment of shade areas. By combining these tactics, an acceptable turf with minimum invasions of ground ivy, violets and other broadleaf weeds may be created.
Characteristics of ground ivy and violets Ground ivy, also known as creeping charlie, needs little introduction to most people in the northern United States. A member of the mint family with the botanical name, Glechoma hederacea, ground ivy has square stems and an aggressive growth habit. The leaves, from 1/2 to 1 1/2 inches in diameter, are arranged opposite of each other along stems and are round to somewhat kidney-shaped with rounded, toothed margins. The medium- to dark-green leaves have a minty odor when crushed. The petioles (leaf stalks) are long. They also have small, funnel-shaped, lavender or purplish-blue flowers, usually appearing from April to June.
Ground ivy forms extensive patches as it creeps along the soil in shaded areas, often advancing into sunny areas as well. They may develop roots at the nodes. Try to pull up a plant - often a series of trailing stems comes up. Ground ivy reproduces both by seed and vegetatively from pieces of roots from broken stems. Poorly drained, fertile soils in shade are typical sites for ground ivy to develop into a major problem.
Violets (Viola spp.) include several cool-season annuals and perennials of the family Violaceae. As a group, these species are low-growing, shade-tolerant and prefer moist, fertile soils. You will see violets most often during cool weather in spring and fall. Leaves of common violet range from 2 to 4 inches in width, are oval to kidney-shaped and feature a heart-shaped base. Petioles are long, slender and slightly hairy. Flowers usually appear in spring and may appear white, blue, purple or yellow. All violets reproduce by seed, but perennial violets may also spread by creeping roots and rhizomes.
Turf care modifications for shade - Use shade-tolerant turfgrasses. Ground ivy and violets are well adapted to shade - lawn grasses are not. Keep in mind, even though a grass may be called shade-tolerant, it still needs a considerable amount of light to achieve acceptable growth. If you are asked to establish a shade lawn, choose a shade-tolerant grass mixture - it is critical. When renovating a shade lawn, add species and cultivars that are better adapted to shade so that existing grasses in a thinning stand can be replaced.
Fine leaf fescues are known for their shade tolerance. Tall fescue and perennial ryegrass have intermediate tolerance, but Kentucky bluegrass is known to have relatively poor shade tolerance. Tolerance varies among cultivars within species as well, so check with your seed supplier for suitable types.
Poa trivialis, or Rough bluegrass, and Poa supina are two additional species that could be the right fit for your shade situation.
- Minimize stress. Turf in shade does not tolerate or recover well from stresses such as traffic and heavy use, while lawns growing in full sun may be able to handle or recover quite well from the same stresses. Suggest this to clients. They will be using these areas and therefore, they will have the most impact.
- Improve light conditions. Start by pruning trees and large shrubs to allow the maximum amount of light to reach the soil surface. This will also improve air circulation over the site which helps to decrease disease potential by minimizing the amount of time that the grass is wet.
- Improve soil conditions. Aerate the soil to improve drainage or compaction problems. This process will help turf grow vigorously and compete with weeds. The presence of tree roots usually makes major modifications of the soil unrealistic. Be careful not to damage tree roots; most are located in the upper 12 to 18 inches of the soil. This includes both tillage operations and adding significant fill soil over established roots.
- Mow higher than what may be considered normal for sun lawns. Raise mower decks so that the mowing height is 3 inches. This increases the leaf surface area of the grass blades, which helps the grass capture more sunlight. Also, taller grass tends to have root systems that are more extensive.
- Fertilize less in the shade. In shade areas, less photosynthesis occurs because less light is reaching the grass plants. Less photosynthesis equates to less energy production in the plants. Therefore, too much nitrogen can be detrimental to shade lawn species by over-stimulating growth. Over-stimulated grass utilizes energy reserves faster than photosynthesis can replace them and results in poor quality turf. About 1 to 2 pounds of nitrogen per 1,000 square feet per growing season is all that is needed in most cool-season, shade turf.
- Water shade lawns infrequently, but water deeply when you do. Try to minimize the time the grass is wet to minimize disease.
Often, these practices are not enough. Ground ivy and other weeds invade, even with repeated herbicide application or renovation attempts. In these instances, there probably is not enough light, even for a shade-tolerant grass species.
Options include tree removal (generally not popular) or alternatives to turfgrass, such as shade-tolerant groundcovers, ferns, woodland flowers and mulches. In some deep-shade situations, existing ground ivy may actually function quite well as a groundcover. Likewise, violets may be desirable in some woodland settings. Just keep in mind that they can advance into surrounding lawn areas.
Control options for existing weeds As with most weed problems, one control option is hand-removal of existing ground ivy or violets. Pull up all of the roots and stems or the plant will grow back. The nature of these species, in particular ground ivy, makes success by hand-removal difficult.
Chemical options are an important part of a total management program. Use post-emergence broadleaf herbicides to control existing ground ivy and violets. Make multiple applications if necessary. Some materials may only give partial control or suppression. Since these are difficult weeds to control, don't make claims of total eradication to clients.
Choose both the proper herbicide and time of applications. They are important factors in obtaining acceptable control of these species. Also, the use of ester formulations may prove to be more effective than amine formulations. Esters tend to penetrate weeds better, but their volatility makes them more prone to damage nearby ornamentals. Therefore, their use may need to be limited to cooler times of the year.
Several herbicide possibilities exist for control of ground ivy. Use three-way broadleaf herbicide combinations that include 2,4-D, mecoprop (MCPP) and dicamba - they provide good control. Herbicides containing 2,4-DP (dichlorprop) or triclopyr may also be effective on ground ivy. Check product labels for the active ingredients, many broadleaf herbicide combination products are available.
For violets, use broadleaf herbicides containing triclopyr and clopyralid or combinations of 2,4-D and triclopyr. They also may require multiple applications for control. Herbicides containing combinations of 2,4-D and 2,4-DP may provide partial weed control. The table on page 38 lists herbicides that control both ground ivy and violets. Refer to the Herbicide Update on page 49 to find chemicals labeled separately for ground ivy or violets.
Mid-spring to early summer and mid- to late fall are favorable time periods for control. Make applications when the plant is in bloom and also around the first frost. At these times, the plant is most susceptible to herbicides. Regardless of the time, make sure the weeds are actively growing. Soil moisture levels should be adequate, and you should refrain from mowing a few days before and after the herbicide application. Finally, always read and follow label directions closely to get acceptable control and avoid any application problems.
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