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Control of Perennial Weedy Grasses in Turf Zac Reicher and Clark Throssell Purdue University Turfgrass Specialists

AY-11

Perennial grasses are especially troublesome in turf areas because few herbicides will selectively control them. The weedy grasses often disrupt the uniformity of a turf area with their different colors, textures, or growth habits.

Distinguishing perennial grassy weeds from other weeds is very important because control measures differ markedly. When establishing or renovating a turf area, it is essential that perennial weeds are identified to maximize the optimum time for control.

Perennial grassy weeds can be grouped into two main categories. Bunch-type grasses, which include tall fescue and orchard grass, can be controlled quite easily. Spreading grasses, such as bentgrass, nimblewill, quackgrass, bermudagrass, and zoysia, are more difficult, if not impossible, to control.

Bunch-type grasses
Tall fescue is a coarse-textured grass, often used as a primary turf species. Tall fescue infestations often result from contamination in a lower quality seed source. Tall fescue leaves are rolled in the bud shoot, and the stem bases are often reddish-colored. The leaf blade is flat with prominent veins on the upper surface; it has a pointed tip.

Orchardgrass is also a bunch-type grass, like tall fescue, with a coarse, upright growth habit. Orchardgrass has very compressed, flat stem bases, is folded in the bud shoot, has no auricles, and has a long, membranous ligule. Infestations are also usually the result of contaminated seed lots.

When there are few weedy patches, bunch-type grasses can best be cut out with a shovel. Be sure to cut down three to four inches into the soil to get all the stems. The holes should be refilled and seeded or sodded immediately. The seed and soil should be representative of that already in the area. If the area has a large number of plants, chemical control will be more efficient. A nonselective systemic herbicide such as glyphosate (Roundup or Kleenup) or glufosinate (Finale) can be spot-applied. These herbicides will also kill the desired turf species; use care during application. The area should be reseeded 5 to 7 days following application. Stir up the soil by raking or chopping to insure good seed-soil contact. Refer to AY-13, "Turfgrass Renovation," for further information concerning renovation.

Chlorsulfuron is a selective herbicide registered for the control of tall fescue in many turf species. Chlorsulforon is available to professional turf managers but not available to homeowners; however, professionals can be hired to apply this chemical. Spot apply chlorsulfuron according to label instructions. The tall fescue will gradually thin and die, allowing the desired species to fill in. Reseeding should not be needed. Do not apply chlorsulfuron to perennial ryegrass. Perennial ryegrass is very susceptible to chlorsulfuron damage.

Spreading Grasses
Creeping bentgrass is a desirable species on golf courses greens, tees, and fairways but is considered a weed in higher-mowed turfs. It is often found in circular patches growing over the top of the desired species. Bentgrass can be identified by its fine texture and spreading growth habit. It has rolled vernation, membranous ligules, prominent veination on the upper surface of the leaves, and pointed leaf tips.

Nimblewill is a weed that resembles creeping bentgrass. It has thin, flat, leaves with four veins on the upper surface; its leaves are usually less than 2 inches long. The hard, thin stems often lie flat on the ground near the base and become upright farther up the stem. The shoots root at the lower nodes; even so, it does not form a mat like bentgrass will. Nimblewill will turn brown at the first frost and is very slow to green up in the spring. The brown patches seen in lawns in the early spring may be nimblewill contamination. Spread is mostly due to seeds produced in the early fall.

Quackgrass has an extensive underground growth habit (rhizomatous) which makes it especially difficult to control. It is easily distinguished by its clasping auricles; leaves are wide and dark green with fine ribs.

Bermudagrass is a warm season turf species that thrives in warm temperatures and will outcompete other desirable species during the summer months. Bermudagrass is classified as a weed because it is slow to green up in the spring and turns brown at the first frost. The stiff leaves are thin, tapering to a point. The ligule is a fringe of long hairs. Bermudagrass is very aggressive and spreads rapidly with creeping flat stolons and/or scaly rhizomes that root at the nodes.

Zoysiagrass resembles bermudagrass closely and is also a warm-season grass species. Zoysia has a rolled vernation as opposed to the folded vernation of bermudagrass. The leaf blades are slightly wider than bermuda, but the rest of the characteristics are basically the same.

Control of spreading grasses is usually attempted with a nonselective systemic herbicide like glyphosate. Gluphosinate, on the other hand, is not systemic in the plant and will not provide effective control of spreading grasses. Best results are seen when the weedy plants are young, fully green, actively growing, and not under drought stress. The mother plants are easily killed, but often the weed will regrow from the stolons or rhizomes. To overcome this, more than one application is recommended. One must allow the weed to regrow before the next application. At least two applications are recommended, but three or more may be needed. One must realize that the area will be dead and unsightly for a number of weeks or months if optimum control is desired.

If there is only a small number of weeds, spot applications can be made with a wick applicator or a small sprayer. Reseeding can take place five to seven days following final herbicide application. This method can be effective, even though undetected weeds will continue to spread across the area.

Once the area has been infested with a large number of weeds, killing the entire area will be most effective. If a herbicide such as glyphosate is used, a number of applications will be necessary. Renovation can begin five to seven days following final glyphosate application. Refer to AY-13, "Turfgrass Renovation" for information on reestablishment.

Fumigation is probably the most effective way of eradicating perennial grassy weeds. Fumigation of the infested areas will kill stolons and rhizomes, eliminating repeated herbicide applications and reducing the time the area is unsightly. The cost and very limited availability of fumigation precludes its use in most situations and is generally not recommended for homeowners.

Control of perennial grassy weeds is a very difficult and time consuming process. One must weigh the advantages and disadvantages before deciding whether to attempt control. Many homeowners may be better off just tolerating perennial grassy weeds in your lawn.

  Purdue University

Indiana 47907

3/98

Cooperative Extension work in Agriculture and Home Economics, state of Indiana, Purdue University, and U.S. Department of Agriculture cooperating;
H. A. Wadsworth, Director, West Lafayette, IN. Issued in furtherance of the acts of May 8 and June 30, 1914.
The Purdue University Cooperative Extension Service is an equal opportunity/equal access institution

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