Managing Weeds in Fescue Lawns

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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.

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.

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.

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 2 and 3½ inches and frequently enough so that no more than 1/3 of the blade is removed. Proper mowing heights will encourage a dense, healthy stand.

When fescue shows sign of drought stress, water deeply so that the entire root zone is wet. During dry periods, this will be every five to six days. This practice encourages a healthy root system. 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.

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 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 you can also find them as a liquid.

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 1 for the coastal and central regions and 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 15 through October 1 for the coastal and central regions and 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 nine weeks after the first.

The following preemergence herbicides (see table 1) are examples of those safe to use on fescue. The first name given is the common name for the active ingredient. The second name is a trade name.

Postemergence herbicides target visible weeds. They are used primarily against broadleaf weeds, perennial grasses, and sedges. The chemicals 2,4D, dicamba, carfentrazone, triclopyr, clopyralid, MCPP and MCPA are broadleaf herbicides. They have been combined in many products that control many broadleaf weeds. Look for these active ingredients in products such as Weed-B-Gon, Weed Killer for Lawns, Bayer Advanced Southern Weed Killer for Lawns, Trimec Southern and many others.

In fescue lawns, grassy weeds such as crabgrass, goosegrass, and dallisgrass can also be controlled with postemergence herbicides. Products containing MSMA (MSMA Turf, Target MSMA and others), CMA (Calar, Ortho Crabgrass Killer-Formula II and others), and fenoxaprop (Acclaim Extra) are recommended.

There are few herbicides that will suppress bermudagrass without harming fescue. Fluziafop, the active ingredient in Fusilade T&O, and fenoxaprop, the active ingredient in Acclaim Extra, are available. These 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 Manage, is effective against both and is safe to use on fescue.

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.

Special precautions have to be taken when treating weeds in newly established lawns. Preemergence herbicides can be applied to newly seeded lawns at ½ the rate recommended for established lawns, but only after the seedlings are 3 inches tall. If seeding after applying a preemergence herbicide, you must wait at least nine weeks. Check the label of the specific product used.

It should be noted that Tupersan can be applied at seeding. It is a preemergence herbicide that will control crabgrass, foxtail and other weeds.

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 one 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.