Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
5/31/99
Contacts:
Richard Jauron , Extension Horticulture, (515) 294-1871,
rjauron@iastate.edu
Elaine Edwards, Extension Communication Systems, (515)
294-5168 eedwards@iastate.edu
Yard and Garden column for the week beginning June 4
Control of Pernicious Lawn Weeds
By Richard Jauron
Extension horticulturist
Iowa State University Extension
A well maintained lawn is an attractive component of a home landscape. Unfortunately weeds can be a problem. Good cultural practices, such as proper mowing, fertilization and watering, will prevent many weed infestations. Herbicides also can be used to control weeds in the lawn. Some weed species, such as dandelion, plantain, white clover and crabgrass, are easily controlled with the proper herbicide. Others are much more difficult to control. Pernicious lawn weeds include quackgrass, nimblewill, ground ivy and wild violets.
Quackgrass
Quackgrass (Agropyron repens) is a cool-season perennial grass. It spreads rapidly by underground stems or rhizomes. Its leaf blades are bright green, coarse in texture and twice the width of bluegrass leaves. Quackgrass is objectionable in lawns because of its coarse texture and spreading habit. Quackgrass also can be a major problem in flower and vegetable gardens.
Nimblewill
Nimblewill (Muhlenbergia schreberi) is a warm-season perennial grass. Nimblewill is a thin, wiry grass that is pale green or gray-green. It spreads by aboveground shoots or stolons, often forming circular spots in the lawn. Nimblewill is easy to spot in the lawn because it greens up late in the spring and turns brown in early fall. Nimblewill is objectionable in the lawn because of its gray-green color and delayed green-up in spring and early browning in fall.
Ground Ivy
Ground ivy (Glechoma hederacea), often referred to as "creeping charlie," is a low- growing, spreading invasive perennial. It spreads by seed and the vining stems that root at their nodes. The leaves of ground ivy are round or kidney-shaped with scalloped margins. Stems are four-sided. Flowers are small, funnel-shaped and bluish purple in color. Ground ivy thrives in damp, shady areas, but also grows well in sunny locations. A member of the mint family, ground ivy produces a minty odor when cut or crushed.
Wild Violets
Several species of violet (Viola species) are native to Iowa. Violets are low-growing, clump-forming plants. They typically bloom in spring (April to June). Flower colors include nearly white, yellow, blue and purple. A few are bicolored. The fruit is a small capsule that splits into three parts at maturity. Wild violets are common weeds in lawns, especially in shady locations.
Control
The best way to control quackgrass, nimblewill and other undesirable perennial grasses is to spot treat the weed-infested areas with glyphosate (Roundup, Kleenup, etc.). Glyphosate is a systemic, nonselective herbicide that is absorbed through the foliage and translocated to all parts of the plant. Visible symptoms (yellow or browning of foliage) usually develop in 7 to 10 days of the application. Plants treated with glyphosate typically die in 2 to 3 weeks.
Gyphosate is most effective when applied to actively growing plants. Midsummer is an excellent time to control undesirable perennial grasses in the lawn. Most perennial grasses, such as nimblewill, are actively growing in summer. Also, midsummer control efforts allow adequate time to kill the weedy grasses and prepare the areas for seeding or sodding in late summer. Complete destruction of the weeds is necessary to prevent their reappearance. Spray the weedy patches and 6 to 12 inches beyond these areas to ensure their complete destruction. A second application will be necessary if the treated areas are not dead in 2 to 3 weeks.
The key to controlling ground ivy is the use of the proper broadleaf herbicide. The most effective broadleaf herbicide products are those that contain dicamba. Two widely sold products that contain dicamba are Trimec and Weed-B-Gon Lawn Weed Killer 2. Fall (mid-September through early November) is generally the best time to control ground ivy. Two applications are usually necessary. The second application should be 10 to 14 days after the first.
The commonly used broadleaf herbicides (2,4-D, MCPP and dicamba) will not effectively control wild violets. Probably the best way to control a small infestation of violets in the lawn is to dig them up.
Once the weeds have been destroyed, good cultural practices and the establishment of a thick, healthy lawn will reduce future weed problems. Also, be vigilant. Ground ivy, quackgrass and other pernicious weeds may reappear. Destroy them quickly before they become major problems.
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