Standing Tall

Tall fescue is a cool-season perennial grass that has gained popularity with homeowners in some regions of the United States due to its year-round color and relatively good heat tolerance. It is commonly grown in the mid-Atlantic region, transition zone and the upper portion (upper Piedmont and mountains) of the warm-humid zone of the mainland United States. Tall fescue also has the ability to survive arid climates when properly irrigated. However, tall fescue often becomes susceptible to leaf spot diseases, brown patch diseases and white grub damage when improperly irrigated or fertilized. Due to the thinning of tall fescue stands following disease or white grub damage, opportunistic weeds such as crabgrass and bermudagrass are able to invade. Furthermore, many of today's housing subdivisions are established on previous bermudagrass fields and pastures, which provides an inherent source of bermudagrass contamination in fescue lawns.

If you're maintaining lawns composed of tall fescue, you need a way to manage bermudagrass — especially during the heat of summer. Being a cool-season grass, tall fescue's optimum temperature for growth is between 65° and 75°F, whereas bermudagrass, a warm-season grass, is best adapted to temperatures between 80° and 95°F. Therefore, during the hot summer months, tall fescue is at its weakest and begins to decline with growth slowing considerably. Meanwhile, bermudagrass and crabgrass grow very aggressively during summer and possess the ability to crowd out the tall fescue during this time. The following discusses tall fescue management and bermuda-grass control strategies for tall fescue stands.

CULTURAL CONTROL

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Strategic manipulation of several cultural practices can encourage tall fescue growth over bermudagrass or crabgrass. The primary cultural practices involve proper seeding rates, fertilization, mowing heights and irrigation programs.

SEEDING RATES

When establishing a turf area, you should apply sufficient tall fescue seed; however, seedlings often become weak, spindly and susceptible to Pythium and other diseases if you use excessive rates. Soils that are fully covered with healthy fescue are better able to crowd out bermudagrass than partially covered soils. An initial tall fescue seeding rate of 5 to 8 pounds per 1,000 square feet is recommended by most turf specialists. In addition, you should seed in the fall as opposed to the spring because it provides the tall fescue more time to mature prior to summer stress.

FERTILIZING

You should base your fertilization program on soil tests and desired appearance. Tall fescue is tolerant of low soil-fertility levels; however, most turf specialists recommend 2 to 4 pounds of nitrogen (N) per 1,000 square feet per year. Turfgrass managers normally apply 0.5 to 1 pound of N per 1,000 square feet two or three times in the fall and winter (September to February) at six- to eight-week intervals. Heavy nitrogen fertilization in late spring or summer increases the susceptibility to heat, disease and drought-stressed turf, which promotes the invasion of summer weeds.

MOWING HEIGHT

When mowed at 2 to 2.5 inches, the new turf-type tall fescue cultivars will grow better, and further increasing the mowing height during dry periods in the summer and under heavy shade may be beneficial. Kentucky 31, the older tall fescue cultivar, should be mowed at 3 inches. Mow frequently enough so that no more than ⅓ of the leaf blade is removed per mowing, and use a rotary mower with sharp blades. For example, if you are maintaining tall fescue at 2 inches, mow it at (or before it reaches) 3 inches. This height encourages maximum root growth and provides a dense canopy to help shade and discourage bermudagrass invasion. When tall fescue is scalped, the thinning of the turf exposes the soil to sunlight which dramatically increases the potential for weed occurrence.

IRRIGATION

You already know that irrigation is an important part of any turf program because irrigation is necessary to replenish water lost via evapotranspiration. But just irrigating isn't an efficient use of your time or water. A proper irrigation program can provide quality turf with minimum water use. Irrigating to prevent drought stress on an as-needed basis is essential for the conservation of water. Irrigate when 30 to 50 percent of the turf begins to wilt, turns blue-green in color or when recovery from foot or tire tracks is slow. Apply enough water to replace the water lost through evapotranspiration and do not irrigate again until the turf shows signs of drought or wilting (approximately every seven to 14 days in winter and three to four days in mid-spring to early fall, depending on cultural practices and soil type). Approximately 0.75 inch of water is needed for each irrigation period to rewet the top 4 to 8 inches of the root zone for most soils, which is equivalent to 465 gallons per 1,000 square feet. The time required to achieve an average of a 0.75-inch depth of water is the time period that you should use for each irrigation period. The length of the irrigation period to apply 0.75 inch of water should remain constant year round, with the only change being the irrigation frequency. Therefore, irrigation programs set by automatic timers should only apply 0.75 inch of water once drought symptoms appear, not on a daily schedule. Light, frequent (daily) irrigation will eventually weaken tall fescue and encourage brown patch disease as well as invasion of bermudagrass, crabgrass, and other weed species.

HERBICIDE CONTROL

Selective control of grassy weeds in tall fescue remains difficult to completely achieve with postemergence herbicides because of unacceptable or unpredictable tall fescue phytotoxicity. Herbicide rates, therefore, have to be reduced, increasing the number of applications required, often lowering bermudagrass control. Only three currently available herbicides provide bermudagrass suppression with a minimal amount of phytotoxicity to fescue. The most widely used is Acclaim Extra 0.57EC (fenoxaprop-ethyl). Acclaim Extra 0.57EC is applied at 1.5 parts product per acre every four weeks beginning after bermudagrass greenup in spring. Do not apply to moisture- or heat-stressed turf or weeds. During summer stress, you may have to lengthen application intervals or reduce rates. Young, actively growing weeds are easiest to control; thus, apply in late spring or early summer to actively growing bermudagrass. Control is reduced if applied within 14 days after a broadleaf herbicide. Tall fescue seedlings should be at least four weeks old prior to treatment. Do not tank-mix with phenoxy herbicides or mow for 24 hours after application.

Turflon Ester (triclopyr) is another herbicide used for selective bermudagrass control with minimal phytotoxicity to tall fescue. Turflon Ester 4EC is applied at 32 ounces product per acre and should be initially applied at the start of bermudagrass greenup in spring with sequential applications being made every four weeks. Minor, short-term tall fescue phytotoxicity may occur when Turflon Ester is applied to heat- or moisture-stressed turf.

The other postemergence herbicide for selective bermudagrass control in tall fescue is Fusilade T&O II 2EC (fluazifop-butyl) at 6 ounces of product per acre. Add a nonionic surfactant at 0.25 percent volume per acre. Similar to Acclaim Extra and Turflon Ester, you should make the first Fusilade application in the spring after bermudagrass greenup followed by sequential applications every four weeks throughout the summer. Minor, short-term turf phytotoxicity may occur, especially if you make these applications during hot, dry weather. However, as Table 1 (page C4) indicates, little, if any, long-term phytotoxicity is normally exhibited with either herbicide. Fusilade T&O II 2EC is no longer registered for home lawn use.

PERSISTENCE IS CRITICAL

No herbicide will consistently control bermudagrass with one application or even with only one year's use. For example, in previous research studies, four to six repeat applications of Acclaim Extra at three- to four-week intervals were needed over two years for satisfactory (about 85 to 95 percent) bermudagrass control. This program is most successful when integrated with an agronomic scheme as described earlier promoting tall fescue growth over the bermudagrass.

Table 1 (page C4) demonstrates the need for persistence with these herbicides. Sixty-three percent bermudagrass control followed one application of Fusilade II at 6 ounces per acre, 77 percent control with two applications (data not shown) and 98 percent control with four and six applications. Similar trends also follow single vs. sequential Acclaim Extra and Turflon Ester applications. In a 2002 research study at Clemson University (see Table 2, page C10), bermudagrass control was slightly inconsistent with those found in 2004 (see Table 1, page C4) following the first four applications; however, September and October applications showed a similar increase in bermudagrass control as recorded in Table 1.

TANK MIXING HERBICIDES

In the infinite search for the miraculous combination of products to provide selective bermudagrass control, various tank-mix combinations have been tried. Acclaim Extra provides good bermudagrass control at the normal row crop rates (63 to 189 ounces per acre); however, these rates often cause undesirable phytotoxicity to the fescue, especially following summer applications.

Two herbicides used in combinations with Acclaim Extra are Prograss 1.5EC (ethofumesate) and Turflon Ester (triclopyr). Six monthly applications of Acclaim Extra 0.57EC at 24 ounces per acre plus Prograss 1.5EC at 174 ounces per acre tank-mixed during one year provided 78 percent common bermudagrass control. Tank-mixed application of Acclaim Extra 0.57EC at 24 ounces per acre plus Turflon Ester 4EC at 32 ounces per acre provided up to 100 percent control with six repeat applications in one year.

Table 1 (page C4) lists a 2004 study conducted at Clemson University comparing applications of Fusilade II, Acclaim Extra, Turflon Ester, Prograss and various tank-mixes of these herbicides. Following three applications, Fusilade II, Fusilade II plus Prograss, Acclaim Extra plus Prograss, Turflon plus Prograss, and Acclaim Extra plus Turflon all provided greater than 80 percent bermudagrass control. Following six monthly applications, all treatments and treatment combinations provided greater than 70 percent bermudagrass control with the exception of Prograss alone. Fusilade II, Acclaim Extra, Turflon Ester and combinations with Prograss provided greater than 90 percent bermudagrass control with acceptable tall fescue turf quality.

THE WHOLE PACKAGE

Bermudagrass is a common problematic weed in tall fescue when grown in the transition zone of the United States. A combination of proper cultural practices and herbicide applications are considered necessary for satisfactory control. To promote a more competitive turf, you should mow tall fescue at its higher height range, fertilize it at the lower rate, and water it heavily but infrequently. Repeat application of any herbicide for at least two consecutive years may be necessary for satisfactory control. Turflon Ester and Fusilade II provide the best control with a minimal amount of tall fescue injury. Four to six applications per year at four-week intervals are needed for satisfactory control and should begin in spring once the bermudagrass shows signs of growth. Tank mixing Acclaim Extra 0.57EC at 24 ounces per acre with Turflon Ester 4L at 32 ounces per acre or Prograss 1.5EC at 174 ounces per acre generally provides better control than using Acclaim alone.

Table 1. Bermudagrass control in tall fescue following one year's (2004) use of Fusilade, Acclaim Extra, Turflon Ester, Prograss and various tank-mixes.
Herbicide(s) Rate Application Timing Bermudagrass Control (%)†† Tall Fescue Quality (1-9)*
5/19/2004 8/18/2004 10/21/2004 5/19/2004 8/18/2004 10/21/2004
Untreated --- --- 0.0 0.0 0.0 9.0 7.5 9.0
Fusilade II 2EC† 6 oz/a 5/4/2004 fb
6/5/2004 fb
7/5/2004 fb
8/4/2004 fb
9/5/2004 fb
10/4/2004
63 98 98 8.8 7.5 8.5
Acclaim Extra 0.57EC 24 oz/a 50 63 72 8.6 7.3 8.7
Turflon Ester 4EC 32 oz/a 17 57 93 8.1 7.2 8.3
Prograss 1.5EC 174 oz/a 10 27 13 8.3 7.0 8.5
Fusilade + Prograss 6 oz/a + 174 oz/a 63 85 97 8.3 7.0 8.5
Acclaim Extra + Prograss 24 oz/a + 174 oz/a 70 78 78 8.1 7.0 8.5
Turflon Ester + Prograss 32 oz/a + 174 oz/a 50 73 100 8.1 7.0 8.5
Acclaim Extra + Turflon Ester 24 oz/a + 174 oz/a 70 67 100 8.1 7.0 8.3
†Fusilade II 2EC is not registered for home lawn use.
††Bermudagrass control was visually rated from 0 to 100% with 0=no control, 90=minimum acceptable and 100=complete control.
*Tall fescue quality was visually rated from 1 to 9 with 9=best and 7=minimum acceptable. fb=followed by.

Table 2. Bermudagrass control in tall fescue following one year's use (2002) of Fusilade, Acclaim Extra, Turflon Ester, Prograss and various tank-mixes.
Herbicide(s) Rate Application Timing Bermudagrass Control (%)†† Tall Fescue Quality (1-9)*
6/5/2002 9/24/2002 10/17/2002 6/5/2002 9/24/2002 10/17/2002
Untreated --- ---
5/22/2002 fb
6/24/2002 fb
8/3/2002 fb
9/3/2002 fb
10/2/2002
0.0 0.0 0.0 9.0 9.0 9.0
Fusilade II 2EC† 6 oz/a 13 92 92 7.0 3.3 3.3
Acclaim Extra 0.57EC 24 oz/a 15 22 22 8.2 9.0 9.0
Turflon Ester 4EC 32 oz/a 8 10 10 8.7 9.0 9.0
Prograss 1.5EC 174 oz/a 4 12 12 7.0 8.3 8.3
Fusilade + Prograss 6 oz/a + 174 oz/a 13 82 82 7.0 8.0 8.0
Acclaim Extra + Prograss 24 oz/a + 174 oz/a 10 52 52 8.0 9.0 9.0
Turflon Ester + Prograss 32 oz/a + 174 oz/a 17 50 50 8.2 9.0 9.0
Acclaim Extra + Turflon Ester 24 oz/a + 174 oz/a 8/12/2002 fb
9/3/2002 fb
10/2/2002
NA 17 17 NA 8.3 8.3
†Fusilade II 2EC is not registered for home lawn use.
††Bermudagrass control was visually rated from 0 to 100% with 0=no control, 90=minimum acceptable and 100=complete control.
*Tall fescue quality was visually rated from 1 to 9 with 9=best and 7=minimum acceptable. fb=followed by.

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