Managing Weeds in Fescue Lawns

Revised by Joey Williamson, HGIC Horticulture Extension Agent, Clemson University, 09/12. Revised by Joey Williamson, HGIC Horticulture Extension Agent, Clemson University, 09/09. Originally prepared by Chuck Burgess, HGIC Horticulture Extension Agent, Clemson University, 06/04.

HGIC 2309

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Tall fescue, Festuca arundinacea, is a popular turfgrass grown in the mountains and upper piedmont areas of South Carolina. To keep it looking its best, weeds should be controlled through an integrated approach. This involves knowledge of weed characteristics and the cultural requirements of the turf.

Disadvantages of Weeds

The main reason homeowners want to rid their lawn of weeds is that they are aesthetically disruptive. In other words, weeds are ugly and interrupt an otherwise uniform appearing lawn. Weeds are also fierce competitors and will rob the turf of sunlight, nutrients and moisture. Lastly, weeds have a tendency to spread rapidly. A few left uncontrolled can quickly become a serious problem.

Types of Weeds

Grassy vs. Broadleaf: Grassy weeds are true grasses which emerge from seed as a single leaf. The leaf blades are longer than they are wide and have parallel veins. An example is crabgrass. Broadleaf weeds emerge from seed with two leaves. Leaves have netlike veins and many, like dandelion or clover, have showy flowers.

Annual vs. Perennial: Annuals germinate, grow, and die within a twelve month period. Summer annuals, such as goosegrass, germinate in the spring, grow through the summer, set seed, and die at the onset of cold weather. Winter annuals, such as chickweed, germinate in the fall, grow through the winter, set seed, and die as temperatures rise in early summer.

Perennials grow for two or more years. They reproduce from vegetative parts such as tubers, bulbs, rhizomes, or stolons, though some also produce seed. Examples are dallisgrass, wild garlic, and clover.

Proper Management

Weed control begins with proper management practices, which encourage a dense, healthy turf. A healthy turf shades the soil so that less sunlight reaches the ready to germinate weed seeds. A thick turf also minimizes the space available for weeds to become established.

Proper management practices include mowing, watering, fertilizing, and liming. These are mentioned briefly here but are covered in detail in corresponding HGIC fact sheets. See HGIC 1205, Mowing Lawns, HGIC 1207, Watering Lawns, and HGIC 1201, Fertilizing Lawns.

Tall fescue should be mowed at heights between 2½ and 3½ inches, and frequently enough so that no more than ⅓ of the blade is removed. Proper mowing heights will encourage a dense, healthy stand.

When fescue shows signs of drought stress, water the lawn deeply so that the entire root zone is wet. This is typically 1 inch of irrigation water per week. During hot, dry periods, this may be every five to seven days. This practice encourages a healthy root system. Watering lawns three or more times per week will enhance conditions for weed seed germination and growth. Look for areas that stay excessively wet and make corrections so that water drains or is directed elsewhere. For more information, refer to HGIC 1207, Watering Lawns.

Fertilize and lime at the proper time and according to a soil test. Proper lime application will help to maintain a soil pH where nutrients are readily available to the turf. In general, spring nitrogen fertilization should cease in March.

Control With Herbicides

Even when cultural practices are heeded, weeds can appear. If the number of weeds reaches an unacceptable level and pulling by hand is out of the question, you may want to turn to herbicides. At this point, it is important to know what weed you are trying to control. Local extension offices and publications can aid in identification.

Preemergence Herbicides: Preemergence herbicides are applied to the soil prior to weed seed germination. They provide good control for many annual grassy weeds and are the best weapon against crabgrass. They also control some broadleaf weeds. Most are in a granular formulation, but some are applied as a liquid spray.

Most granular preemergence herbicides should be watered in with about ½ inch of irrigation immediately following application. This activates the herbicide which is absorbed by the young roots and shoots of weeds as they begin to grow.

In the spring, preemergence herbicides should be applied when air temperatures reach 65 to 70 °F for four consecutive days. On average, this is March 15-30 for the piedmont and mountains. In the fall, to control winter annuals, apply preemergence herbicides when nighttime lows reach 55 to 60 °F for four consecutive days. On average, this is September 1 to 15 for the piedmont and mountains.

Preemergence herbicides are generally effective for six to 12 weeks, depending on the product. For season long control, make a second application. Before using, read the entire label and follow it precisely. See Table 1 for specific products.

Table 1. Preemergence Herbicides
Active Ingredients Examples of Brands
pendimethalin Scotts Halts Crabgrass Preventer
dithiopyr StaGreen CrabEX Crabgrass Preventer
Green Light Crabgrass Preventer
benefin plus trifluralin Hi-Yield Crabgrass Preventer
Benefin plus oryzalin XL

Postemergence Herbicides: Postemergence herbicides target visible weeds. They are used primarily against broadleaf weeds, perennial grasses, and sedges. The chemicals 2,4-D, dicamba, mecoprop (MCPP), MCPA, carfentrazone, and triclopyr are broadleaf herbicides. They have been combined in many products that control many broadleaf weeds. Look for these active ingredients in products such as Ortho Weed-B-Gon for Southern Lawns, Spectracide Weed Stop Weed Killer for Lawns, Bayer Advanced Southern Weed Killer for Lawns, Bonide Chickweed Clover & Oxalis Killer, and Ortho Weed-B-Gon Max. Always check the product label to be sure that it can be used safely on a tall fescue lawn, the application rate, and that it will control the specific weeds.

In fescue lawns, grassy weeds such as crabgrass, goosegrass, and dallisgrass can also be controlled with postemergence herbicides. Products containing MSMA (such as Hi-Yield 529 MSMA Weed Killer, Bayer Advanced All-in-One Lawn Weed & Crabgrass Killer, Ferti-lome Crabgrass, Nutgrass & Dallisgrass Killer, and Ferti-lome Improved Bermudagrass Killer), fenoxaprop (such as Bayer Advanced Bermudagrass Control Ready-to-Spray), and quinclorac (such as Spectracide Weed Stop for Lawns Plus Crabgrass Killer, Bayer Advanced All-in-One Lawn Weed & Crabgrass Killer, and Ortho Weed-B-Gon Plus Crabgrass Control) are recommended. Production of MSMA products may end after 2009.

There are few herbicides that will suppress bermudagrass without harming fescue. For home lawns, fenoxaprop, the active ingredient in Bayer Advanced Bermudagrass Control Ready-to-Spray, is available. This should be applied as soon as the bermudagrass turns green in the spring and repeated in two to three weeks. Stop treatments in late May when temperatures consistently reach 85 °F.

Yellow nutsedge and purple nutsedge are difficult to control perennials. Halosulfuron, the active ingredient in Sedgehammer, is effective against both and is safe to use on fescue. Sedgehammer requires the addition of a nonionic surfactant at 2T per gallon of water, and may need to be repeated in 3 to 4 weeks for complete control. Sulfentrazone (one of the active ingredients in Spectracide Weed Stop Weed Killer for Southern Lawns Concentrate) is faster acting on nutsedges, but may also require a second application. Penoxsulam (such as in the granular product Green Light Wipe Out Tough Weed Killer for Lawns) will control annual nutsedges.

Guidelines for Using Postemergence Herbicides

When choosing an herbicide, make sure that it will control the weed and that it is recommended for your turf. Before using, read the entire label and follow it precisely. The following tips will help you achieve optimum control.

  • Most broadleaf weeds are best treated in the spring or fall when air temperatures are between 65 and 85 degrees F. In hotter temperatures, turf damage is more likely.
  • At the time of treatment, soil moisture should be adequate. When drought stressed, weed control is poor and turf damage is more likely.
  • Do not mow immediately prior to or after application. Mowing lessens the amount of surface area that the herbicide contacts.
  • Treat weeds when no rain is expected for at least 24 hours.
  • Avoid treating on windy days because some herbicides can injure ornamental plants.
  • Best results occur when weeds are young.
  • For acceptable control, repeat applications, 10 to 14 days apart, may be required.

Precautions for New Lawns

It should also be noted that there are precautions for new lawns with regard to preemergence use. A new lawn must have time to become well-established, as preemergence herbicides can inhibit lawn grass root growth. Always read the label thoroughly for specifics regarding seeding. On fescue lawns, preemergence herbicides should not be applied in the fall if over-seeding will be done. Any preemergence herbicide application would have to be delayed until spring for summer weed control. To keep a tall fescue lawn thick and more weed-free, consider over-seeding one fall, and alternating that with a preemergence herbicide application the next fall. For bermudagrass lawns to be over-seeded with annual ryegrass, delay seeding until 6 to 16 weeks after the preemergence herbicide application (depending upon rate of application).

Postemergence herbicides can be applied to newly seeded lawns at ½ the rate, but only after it’s been mowed four times. If overseeding after a postemergence herbicide treatment, you must wait three to four weeks, depending on the product used. In sodded areas, preemergence herbicides can be applied following signs of new growth, at ½ the rate recommended for established grasses. Postemergence herbicides should not be applied until the grass is visibly growing and spreading. Use ½ the recommended rate until after the turf has been mowed three times.

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This information is supplied with the understanding that no discrimination is intended and no endorsement of brand names or registered trademarks by the Clemson University Cooperative Extension Service is implied, nor is any discrimination intended by the exclusion of products or manufacturers not named. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.