Managing Weeds in Fescue Lawns

Annual bluegrass (Poa annua) seeds germinate in the fall, and this grassy weed makes white seed heads in the early spring.
Joey Williamson, ©2015 HGIC, Clemson Extension

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

Disadvantages of Weeds

The main reason homeowners want to rid their lawns of weeds is that they are aesthetically disruptive. In other words, weeds are ugly and interrupt the uniform appearance of a lawn. Additionally, weeds are fierce competitors that will strongly compete with the turf for 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

Common dandelion (Taraxacum officinale) seeds blow in the wind and allow this perennial weed to become a frequent invader of home lawns.
Joey Williamson, ©2015 HGIC, Clemson Extension

Grassy vs. Broadleaf: Grassy weeds are true grasses that emerge from seed as a single leaf. The leaf blades are longer than they are wide and have parallel veins. Crabgrass is an example of a grassy weed.

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 are also spread by seed. Examples are dallisgrass, wild garlic, and clover.

Proper Management

Weed control begins with proper management practices, which encourage a dense, healthy turf. Healthy turf shades the soil so that less sunlight reaches the weed seeds, which need light to germinate. 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 mowed frequently enough so that no more than ⅓ of the blade is removed. For turfgrass in partial shade, the mowing heights may be raised slightly. 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 moist. This typically requires 1 inch of irrigation water per week. During hot, dry periods, this may be every five to seven days. One inch of irrigation water will moisten the soil down to 6 inches deep and encourage a healthy, extensive root system. Watering lawns three or more times per week will create moist surface soil conditions, and this will promote 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. When a soil test indicates lime is needed, it is applied to help maintain a soil pH where nutrients are readily available to the turf. In general, spring nitrogen fertilization should cease in March.

Core aeration helps relieve the soil compaction that prevents optimum root growth and favors many weeds. Core aeration is superior to spike aeration. To read more about lawn aeration, please see HGIC 1200, Aerating Lawns.

Control with Herbicides

Even when all cultural practices are employed, some weeds can still appear. If the number of weeds reaches an unacceptable level and pulling by hand is out of the question, one may need to apply herbicides. At this point, it is important to know what weed you are trying to control. Local Extension offices, the Clemson Home & Garden Information Center, the Clemson Plant & Pest Diagnostic Clinic, and state Extension 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 and annual bluegrass. They also control some broadleaf weeds. Most are in a granular formulation, but some are applied as a liquid spray.

Most granular and liquid preemergence herbicides should be watered into the soil with about ½ inch of irrigation water immediately following application. This activates the herbicide, which is absorbed by the young roots of weeds as they germinate and 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 eight or nine weeks after the first. Preemergence herbicides should not be applied to newly seeded or established lawns until rooting and regular growth have taken place. This is typically associated with at least two mowings but can be time-dependent based on the product used. Before using, please read the entire label and follow it precisely. See Table 1 for examples of herbicides and products.

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. Always check the product label to be sure that it can be used safely on a tall fescue lawn, that it will control the specific weeds in the lawn, and that it will be used at the correct rate. With many products, repeat applications in 10 to 14 days may be necessary for difficult to control weeds. For triclopyr, a repeat application may be needed in 4 weeks on some weeds.

In fescue lawns, grassy weeds such as crabgrass, goosegrass, and dallisgrass can also be controlled with postemergence herbicides. Products containing fenoxaprop and quinclorac are recommended.

There are few herbicides that will suppress bermudagrass without harming fescue. For home lawns, the active ingredient fenoxaprop is available. This is best applied as soon as the bermudagrass turns green in the spring and repeated monthly. Stop treatments when temperatures consistently reach 90 °F and do not apply to drought-stressed fescue. The addition of a nonionic surfactant at 2 teaspoons per gallon of water will improve control.

Yellow nutsedge and purple nutsedge are difficult to control perennials. Halosulfuron is effective against both and is safe to use on fescue but will need to be repeated in 3 to 4 weeks for complete control. Some products require the addition of a nonionic surfactant at 2 teaspoons per gallon of water. Sulfentrazone is faster acting on nutsedges but will also require a second application. See Table 2 for examples of herbicides and products to control broadleaf weeds, grasses, and sedges.

Guidelines for Using Postemergence Herbicides

When choosing an herbicide, make sure that it will control the weed and that it is recommended for the specific turfgrass in the lawn. Before using, read the entire label and follow it precisely for rate and timing. 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. During hotter temperatures, turf damage is more likely to occur.
• At the time of treatment, soil moisture should be adequate. When stressed by drought, weed control is poor, and turf damage may occur.
• Do not mow immediately prior to or after application. Mowing lessens the amount of weed leaf surface area that the herbicide contacts.
• With spray applications, treat weeds when no rain is expected for at least 24 hours.
• Avoid treating on windy days because herbicide spray drift can injure ornamental plants.
• The best results occur when weeds are young.
• For acceptable control, repeat applications may be required. The product label will tell when to retreat the weeds.

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 the lawn is to be over-seeded. If over-seeded by October, any preemergence herbicide application would have to be delayed until spring (March) 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. In sodded areas, preemergence herbicides should be used only on well-established turfgrass tall fescue.

For bermudagrass lawns to be over-seeded with annual ryegrass, delay seeding until 6 to 16 weeks after the preemergence herbicide application (depending upon the rate of application and the herbicide used).

Postemergence herbicides can be applied to newly seeded lawns at ½ the rate, but only after the lawn has been mowed four times. If overseeding after applying postemergence herbicide treatment, wait three to four weeks, depending on the product used. Postemergence herbicides should not be applied if summer temperatures exceed 90 °F.

Table 1. Preemergence Granular Herbicides for Lawns.

Table 2. Postemergence Herbicides for Tall Fescue Lawns.

Pesticides are updated annually. Last updates were done on 11/22 by Adam Gore.

Originally published 06/04