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MTC Turf News – Dr. Tom Turner, University of Maryland and Dr. Joe Roberts, University of Maryland

Turf-type tall fescue has become the predominant species recommended and used for lawns in Maryland. It is also commonly used on athletic fields, institutional grounds, roadsides, and golf course roughs.

Before the early 1980’s, only one tall fescue, Kentucky 31, was commonly used for turf areas. Its coarse texture, yellowish green color, and lack of dependable seed quality limited its use. Kentucky 31 did not have acceptable quality for most homeowners and is considered primarily a forage grass. However, compared to most other turfgrasses commonly used at that time, Kentucky 31 did exhibit good drought tolerance, had minimal pest problems, and required reduced maintenance inputs. Thus, turfgrass breeders began intensive efforts on improving the quality characteristics of tall fescue while maintaining or improving upon the desirable characteristics of Kentucky 31. The results have been extremely successful, and numerous excellent turf-type tall fescues are available for homeowner and professional use.

Some of the characteristics of turf-type tall fescue include:

1. Excellent in full sun to moderate shade
2. Excellent drought tolerance
3. Excellent tolerance to disease and insect problems
4. Minimal weed problems when maintained properly and mowed at recommended heights
5. Very good wear tolerance
6. Moderate fertility requirements, which become lower as the turf matures
7. Rapid establishment from seed
8. Excellent availability of seed for recommended cultivars
9. Excellent availability of sod certified by the Maryland Department of Agriculture
10. Very good density, which helps maximize water infiltration and minimize runoff
11. Thatch production not a problem

Selecting Cultivars

         One of the most critical factors in long-term successful turfgrass management is the selection of cultivars that have been shown to persist in this region. Maryland and Virginia cooperate in extensive cultivar testing. Researchers from University of Maryland and Virginia Tech meet annually to review cultivar research data in these states from the National Turfgrass Evaluation Program (NTEP), Cooperative Breeders Tests, and joint MD-VA trials. The list of recommended cultivars is published annually in University of Maryland Turfgrass Technical Update #77 “Recommended Turfgrass Cultivars for Certified Sod Production & Seed Mixtures in Maryland”. The current recommended cultivars are shown in Table 1. Proven cultivars are those that have performed well in research and have had certified seed tested by the Maryland Department of Agriculture (MDA). Promising cultivars are those that have performed well in more recent cultivar trials, but for which certified seed has not been tested by the MDA. Sod certified by the MDA must contain cultivars on the recommended list.

Table 1. Recommended Turf-Type Tall Fescue Cultivars (2018)

Proven Cultivars

Promising Cultivars

Mixing with other Turfgrass Species

         Although monostands of turf-type tall fescue perform very well in Maryland, many seed mixtures may contain other species. The only other turfgrass species that we recommend to be mixed with tall fescue is Kentucky bluegrass (using recommended cultivars). Tall fescue – Kentucky bluegrass mixtures have performed very well and may have overall improved disease tolerance and recuperative capacity compared to tall fescue alone. It is, however, very important to limit the amount of Kentucky bluegrass included in these mixtures. For home lawn and professional seed mixtures, the amount of Kentucky bluegrass should be limited to 3-5% by weight of the seed mixture, whereas up to a maximum of 10% may be used in mixtures for sod production. Perennial ryegrass should not be mixed with tall fescue, as diseases such as brown patch, red thread, and gray leaf spot may be much more severe compared to tall fescue alone.

Establishment

The preferred time for seeding turf-type tall fescue is late August to mid-October. Natural rainfall tends to be more prevalent during this period and competition from weeds tends to be reduced. Late winter and early spring seeding may be successful, but competition from annual grassy weeds and summer annual broadleaf weeds may be intense. In addition, younger plants going into the summer may be more prone to drought and diseases such as brown patch and pythium. Recommended seeding rates are from five to eight pounds per 1000 ft². Lower seeding rates tend to result in coarser leaf blades, while higher rates offer no long-term benefits. Establishment from sod can be done over a much wider timeframe as long as water is adequate to allow for good rooting of the sod.

Mowing

Proper mowing is essential in maximizing the beneficial characteristics of turf-type tall fescue. Of greatest importance is mowing height, which should be in the range of 2 ½ to 3 ½ inches. Many homeowners mow the lawn too low. Mowing at 2 inches or lower weakens turf, reduces root systems, and greatly increases the eventual encroachment of weeds into the lawn. Low mowing heights can also increase the incidence and damage of other pest problems while reducing drought tolerance.

Frequency of mowing should be a function of the growth rate of the lawn. The amount of mowing during a season can be reduced if mowing is done on an as-needed basis, not on a set schedule.

Turf-type tall fescue can grow relatively fast in early spring and fall. When possible, try not to cut off more than 1/3 of the grass height in any one mowing. Thus, if you are maintaining a 3-inch height, try to mow before the grass exceeds a height of 4 inches. During the summer or during dry periods, tall fescue may be growing much more slowly and frequency of needed mowing may be substantially less.

Clippings should normally be left on the lawn and are usually beneficial. The only time that clippings need to be removed is when the grass has gotten excessively high and large clumps of clippings remain that may smother turf. Recycling of clippings on the lawn can reduce the future need for fertilizer by as much as 25-35%. If clippings are removed, use them for compost. Don’t bag clippings for trash removal unless your community has a program for sending yard waste to a composting facility.

Make sure the mower blades are sharp and are adjusted properly to provide an even cut. Dull blades can shred leaves, which may reduce the visual quality of the turf and increase the incidence of some diseases.

Irrigation

         Most homeowners in Maryland either do not water their lawns or would prefer not to. Turf-type tall fescue has excellent drought tolerance. Although turf-type tall fescue may go dormant during severe droughts, recommended cultivars will typically recover when temperatures moderate and rainfall occurs. Proper irrigation during dry periods, however, can help maintain growth, reduce weed encroachment, and reduce wear from traffic on areas such as athletic fields. Deep, infrequent irrigation (wetting soil to a depth of 3-6 inches) is much preferred to light, frequent irrigation. Irrigation equipment should be adjusted to ensure that water is applied only as fast as can be absorbed by soil to prevent water runoff. Avoid evening and nighttime irrigation, as diseases such as brown patch and pythium are much more likely to be a problem due to extended leaf wetness under these conditions.

Fertilization

         Nitrogen fertilization plays a critical role in the health and sustainability of turf-type tall fescue in Maryland. Due to its impact on turfgrass density, proper N fertility plays a key role in reducing weed encroachment (resulting in reduced need for herbicide applications), improving both wear tolerance and recovery from damage, and reducing water runoff and soil erosion. Recommended total annual N rates are shown in Table 2.

Table 2. Recommended Total Annual Nitrogen Fertilizer Rates for Tall Fescue Turf

Nitrogen fertilizer applications must conform to Maryland Department of Agriculture nutrient management regulations as outlined in University of Maryland Turfgrass Technical Updates. If a soluble N fertilizer is used, no more than 0.7 pounds actual N per 1000 ft² can be applied in any one application. If a slow release N fertilizer source is used, no more than 0.9 pounds actual N per 1000 ft² can be applied in any one application. If an enhanced efficiency N fertilizer source is used, up to 2.5 pounds actual N per 1000 ft² can be applied in any one application, although other restrictions may apply for these fertilizers.

As outlined in Maryland nutrient management regulations, N fertilizer cannot be applied to turfgrass between December 1 and March 1, and a maximum of 0.5 pounds actual N per 1000 ft² can be applied between November 15 and December 1. University of Maryland guidelines generally recommend that 2/3 to 3/4 of the annual N fertilizer be applied between late August and December 1, with the remaining N fertilizer being applied between March 1 and June 1.

Phosphorus, potassium, and limestone applications should be made as recommended by a certified soil testing laboratory.

Diseases of Tall Fescue

There are a variety of common lawn diseases that can occur in Maryland. The incidence of these diseases can be greatly minimized by using turfgrass cultivars that are recommended by the University of Maryland. The extensive turf-type tall fescue cultivar trials conducted at the University of Maryland do not employ any disease control applications and screen cultivars for disease resistance. Also, using recommended mowing, fertilizer, and irrigation practices will greatly help in minimizing any potential disease problems.

Further information on the symptoms of common diseases as well as the cultural practices and, if needed, fungicidal control that help minimize disease severity can be found in the University of Maryland publications located on the Maryland Turfgrass Council website (mdturfcouncil.org). Following is information on some of the most prevalent diseases affecting turf-type tall fescue turfgrass in Maryland:

Rhizoctonia Brown Patch – Brown patch is the most important disease of turf-type tall fescue and is caused by the fungus, Rhizoctonia solani. Ideal conditions for infection include high temperature and humidity conditions that are often observed from June to September. Stand symptoms of brown patch are small circular patches (i.e., 3-6” in diameter) of blighted turf that can appear brown in color (Figure 1). Patches can spread radially when environmental conditions are particularly conducive resulting in larger areas (i.e., >12” diameter) of symptomatic turf. Closer examination of the infected turf in the outer margin of patches can often reveal leaf lesions on individual plants (Figure 2). Plant lesions are often irregularly shaped with a tan-colored center surrounded by a dark brown margin where the lesion meets the green tissue. When high humidity persists or often in the mornings when dew is present, grayish brown mycelium can be observed in the leading margin of the patch (Figure 3). Kentucky bluegrass and perennial ryegrass can also become infected. Perennial ryegrass is particularly sensitive to this disease and can be badly damaged. Spring seedlings of tall fescue are considered more susceptible and while mature tall fescue can also be severely blighted, brown patch is primarily a foliar disease on this species. When weather cools or becomes less humid, the tall fescue turf will generally recover.

Brown patch is more severe under excessive nitrogen fertility in the spring and when turf is irrigated improperly. This disease is most severe when leaf blades stay wet for over 8 hours at night. Thus, if the lawn is irrigated, it is important to make sure leaves have dried before nightfall

Figure 1. Brown Patch (Rhizoctonia solani) disease of tall fescue turf

Figure 2. Brown patch lesions on tall fescue leaves

Figure 3. Mycelium present on foliage during humid periods

Red Thread – Red thread is a very common disease on cool season grasses in Maryland that is caused by the fungus, Laetisaria fuciformis. It is one of the first diseases to appear in early spring and is associated with cool, wet weather in the spring and fall. The symptoms and signs of this disease are among the most distinctive of turfgrass diseases. Initial infection can be observed as straw-colored dead leaves, but in the presence of morning dew or water from rain, a coral pink or reddish layer of fungal growth is often evident on turfgrass leaves (Figure 4). As the turf dries, the mycelium has a pale pink color. During the latter stages of leaf blighting, a bright red thread-like mass of fungal mycelium may be seen extending from leaf tips. Affected turf can have patches of damaged leaves from one to six inches in diameter.

Red thread disease can infect bluegrasses, fescues, and ryegrasses and is usually associated with undernourished turf. Perennial ryegrass and creeping red fescue are often considered the most susceptible and mixtures with these grasses can increase likelihood of disease (Figure 5). Following recommended guidelines for nitrogen fertilization will greatly minimize the occurrence and severity of this disease. If proper fertility is practiced, fungicidal control of this disease is rarely needed.

Figure 4. Pinkish red color associated with red thread disease

turf-type tall fescue                                turf-type tall fescue + perennial ryegrass

Figure 5. The effect of the mixing of perennial ryegrass with turf-type tall fescue on red thread disease

Rust – Rust is a common disease that is caused by multiple fungi. All turfgrass species can become infected, particularly when soil pH is too low or turf is under fertilized. The early symptoms of rust diseases appear as light-yellow flecks on the leaves. As the disease progresses, yellowed flecks will enlarge and develop red, orange, or yellow pustules that can be easily wiped off and produce these colors on your hand (Figure 6). When observed from a distance, the lawn will often have a yellowish or orange appearance while severe infections can cause thinning of the turf canopy. While rust can occur throughout the year, it is most prevalent in late summer and fall. Using recommended cultivars, irrigating to avoid water stress, correcting soil fertility problems as indicated by a soil test, and implementing a sound nitrogen fertilizer program will greatly minimize the occurrence and severity of rust disease on tall fescue lawns.

Figure 6. Rust pustules on turf foliage

Net Blotch – Net blotch occurs on turf-type tall fescue and is similar to leaf spot disease. The symptoms generally occur as very small brown or purple-brown specks on the leaves that may progress to dark brown spots that have a net-like appearance. Symptomatic leaves can have dieback from the tip downward. This disease, while noticeable, rarely causes severe damage to tall fescue. The disease usually appears in the spring or fall when the weather is cool and moist, particularly with extended periods of overcast weather.

Gray Leaf Spot – Gray leaf spot is a disease that occurs on both cool and warm season turfgrasses. It is caused by the fungal pathogen Magnaporthe oryzae and has been well known for causing significant damage to perennial ryegrass but can also be very destructive to tall fescue under ideal environmental conditions. The disease initially appears as temperatures and humidity increase in July. The disease can progress rapidly with frequent rainfall or excessive irrigation as leaf wetness is a driver of disease. Symptoms initially appear as chlorosis with small, circular lesions on the leaves (Figure 7). The tips of infected leaves can appear twisted or flagged (Figure 8) and can progress to a severe decline of entire turfgrass stands. Applying high amounts of soluble-N during times when environmental conditions are conducive for disease can exacerbate disease. Seedlings are also considered more sensitive to infection, so the use of slow-release N is a viable option for fall seedings. Deployment of resistant cultivars is a viable method in reducing gray leaf spot, particularly on perennial ryegrasses where resistance is well documented. The use of susceptible perennial ryegrass in mixed stands with tall fescue can also increase likelihood of tall fescue infection. Regardless, the use of cultivars that are well adapted to the growing environment can reduce turf loss from disease.

Figure 7. Characteristic gray leaf spot lesions on tall fescue leaf blades

Figure 8. Leaf flagging associated with gray leaf spot on tall fescue

Figure 9. General thinning associated with severe gray leaf spot infection on tall fescue

Pythium blight – Pythium blight can occur on all turfgrasses, particularly when turf is subjected to excessive water through overhead irrigation or rainfall. There are numerous Pythium species that can cause blight, which are more prevalent during hot, humid weather. Symptoms can initially appear as small, discolored irregular-shaped spots in the turf canopy that can enlarge rapidly given hot and moist conditions. Given that the pathogen is favored by excessive water, patterns of blight can appear to follow water drainage patterns. Mycelium is often observed in infected areas during the morning hours when the foliage is wet (Figure 10) and can persist well into the daytime if humidity and canopy moisture are high. Similar to gray leaf spot, Pythium blight is more severe in seedlings and is favored by high amounts of soluble-N applied when conditions are conducive to disease. Limiting overhead irrigation to reduce leaf wetness is critical to reducing turf loss from Pythium blight.

Figure 10. Pythium blight symptoms and mycelium observed in tall fescue turf canopy following frequent rainfall