Cool- and warm-season turfgrasses differ in their vulnerability to diseases. In the mid-South, bentgrass suffers from a wide range of diseases. Even in the Midwest and Northeast, this turfgrass will not thrive without an intensive fungicide program. Perennial ryegrass and, to a lesser extent, Kentucky bluegrass, tall fescue and other fescues are occasional targets of diseases. Among warm-season turfgrasses, zoysiagrass and St. Augustinegrass are most vulnerable to diseases. In particular, patch diseases on zoysiagrass, St. Augustinegrass and bermudagrass are relatively common. Well-managed centipedegrass lawns suffer from few diseases. Typically, the more intense the management, the more vulnerable any turfgrass is to damaging diseases.
PYTHIUM BLIGHT AND SUMMER DECLINE
Pythium blight or cottony blight and summer decline are damaging and difficult to control. While all cool-season turfgrasses are vulnerable to Pythium, bentgrass is the primary target. In the mid-South, overseeded perennial ryegrass and Poa trivialis, as well as tall fescue sod fields are also targets. A day or two of heavy cloud cover plus drizzle, showers or heavy dews are a prerequisite for Pythium outbreaks. Up North, cottony blight occurs in mid-summer when night temperatures reach 70°F and moisture requirements are met. Down South, Pythium blight on overseeded turfs occurs in late fall to early spring disease when a mild, very moist air mass is trapped between a warm and cold front. Foliar symptoms of summer root decline occur on bentgrass when afternoon temperatures exceed 90°F for several days. Very high populations of ring or stunt nematode may also be associated with summer decline of bentgrass. High rates of nitrogen also increase vulnerability of cool-season turfgrasses to this disease. Warm-season turfgrasses are rarely damaged by Pythium-incited diseases.
The name cottony or Pythium blight comes from mass of cottony white fungal filaments or mycelia of causal Pythium fungi that is found in early morning in the canopy of blighted turfs when weather patterns favor rapid pathogen growth. On sunny days, these threads disintegrate as the leaves dry. Leaves and shoots of blighted turf, which is first dark-colored and greasy in appearance, later dry and turn light brown. On bentgrass, perennial ryegrass and Poa trivialis, blighted, sunken patches are usually 2 to 3 inches in diameter. Clusters of these blighted circular spots merge, forming large irregular areas of dead turf that often follow drainage or equipment patterns.
As the name implies, summer decline is characterized by a patchwork of chlorotic, thinning and then healthy bentgrass. The crown and roots of declining turf often appear slimy or partially rotted. Classic cottony blight symptoms are not associated with summer decline.
A preventative fungicide program is the best defense against Pythium-incited diseases. Up North, bentgrass must be protected between mid- to late-May until late August or early September. Make applications on a calendar schedule when night temperatures exceed 70°F or according to a Pythium advisory. Further south, the Pythium treatment window must be extended into the fall, spring and possibly winter months. To protect overseeded perennial ryegrass or Poa trivialis fairways in the South, apply a fungicide when favorable weather is forecast or on a calendar schedule but not late enough to interfere with bermudagrass green-up. Due to the risk of fungicide-resistant Pythium strains, always rotate two or possibly three fungicides that have different modes of action. Recommended fungicide chemistries are listed in the table on page 50. Preventative fungicides usually are most effective when they are combined with good management.
Brown patch may be more damaging down South. Down here, this disease is a serious threat to bentgrass greens and tall fescue lawns in the summer, as well as zoysiagrass, St. Augustinegrass and occasionally centipedegrass lawns and sod fields during fall and spring transition. Along the Gulf Coast, brown patch may occur in the winter on green but partially dormant St. Augustinegrass. Bermudagrass is rarely a target of brown patch. While, brown patch on cool-season turfs is strictly a hot, sticky weather disease in the Midwest and Northeast, cool-season yellow patch may appear on Kentucky bluegrass and perennial ryegrass lawns. Regardless of the location, a day or two of cloudy, wet weather conditions are usually needed to trigger a disease outbreak. Excessive or poorly timed nitrogen fertilizer applications increase turf susceptibility to this disease. Once established, brown patch reappears year after year when weather conditions favor disease.
Brown patch first appears as small, circular patches several inches in diameter, which quickly expand from 1 foot on bentgrass to well over 6 feet on St. Augustinegrass. Typically, the coarser the grass is, the bigger the patch. Foliage of higher cut turf usually wilts and collapses, giving the blighted patches a sunken appearance. Leaves and leaf sheaths attached by the brown patch fungus first become water-soaked, wilt and finally turn brown. On bentgrass, a faint “smoke ring” of mycelia may be seen early in the morning but it disappears as the leaf canopy dries. On broadleaf St. Augustinegrass and tall fescue, distinct tan spots or bands bordered by a water-soaked margin are seen. This disease often appears to “move” from a shaded to sunny areas of a lawn.
You can reduce the risk of brown patch by making multiple applications of a lower rate of a fast release fertilizer or use of a slow-release nitrogen source, particularly when weather patterns favor rapid disease development and the target turf is vulnerable. On warm-season turfgrasses, avoid fall and early spring nitrogen applications. Increasing sunlight penetration by removing overhanging branches will also reduce turf susceptibility to brown patch.
With the exception of bentgrass greens and tees during the summer, brown patch outbreaks are too sporadic to justify preventative fungicide treatments. Scout and keep a record of greens and tees, as well as areas of fairways, sod fields or customer lawns previously damaged by brown patch. When the turf is vulnerable and weather favorable, apply a fungicide to the previously damaged areas. Fungicides labeled for brown patch control are listed in the table, on page 50.
OTHER PATCH DISEASES
Patch diseases, which are caused by several ectotrophic fungi, are reported for most intensively managed turfgrasses. Summer patch and necrotic ring spot appear on Kentucky bluegrass, Poa annua and fine fescue turfs. Recently, bentgrass dead spot and take-all patch have been recognized on bentgrass. Spring dead spot (SDS) is a damaging disease on bermudagrass lawns, greens and fairways, particularly where this turf is marginally adapted. On greens, bermudagrass decline is the warm-weather equivalent of spring dead spot. Take-all root rot is a vicious spring and summer disease on St. Augustinegrass lawns. An SDS-like disease on zoysiagrass is not well characterized.
On cool-season turfs, symptoms of summer patch and necrotic ring spot, which are circular to irregular rust to later straw-colored patches ranging from 6 to 12 inches in diameter, appear virtually overnight from June to August on previously healthy Kentucky bluegrass lawns or fairways. A “frog eye” pattern with a small patch of healthy turf surrounded by a ring of bleached grass is often seen. With bentgrass dead spot, circular spots, 1 to 2 inches in diameter, have a tan center with a distinctive reddish-brown outer margin. Take-all on bentgrass is characterized by circular patches of dead turf that initially are about 6 inches in diameter but expand over a period of several years to a diameter of 3 feet.
For spring dead spot, arc-shaped to circular patches of bleached turf, which range for a few inches to several feet in diameter, appear at bermudagrass greens-up. A “frog eye” pattern is seen when bermudagrass or weedy grasses colonize the patch center. While these patches often disappear in the South after two or three months, recovery further north may take several years. Patches often reappear year after year in the same area. Similar symptom patterns are seen on zoysiagrass. Bermudagrass decline is characterized by a yellowing and thinning of irregular patches on greens during the summer. Symptoms are similar to those associated with sting nematode. Severe stand thinning in arc-shaped, circular to irregular patches, which range in size from 3 to 15 feet, occurs on take-all root rot-damaged St. Augustinegrass. Since weeds quickly invade, recovery of the damaged patches is very slow. Damage is heavier in sunny than shady areas.
Symptom severity of many patch diseases may be reduced and recovery accelerated by using acidifying nitrogen sources. Avoid nitrate-based fertilizers. Also, fertilize with low rates of nitrogen frequently enough to maintain a moderate growth rate during the growing season. Using a slow release or an organic nitrogen sources is an option. With SDS-like diseases, do not apply a fast-release nitrogen fertilizer in the fall, especially to previously damaged turfs. Apply nitrogen and potassium in a 1:1 to 2:1 nitrogen to potash ratio. Use the chloride (murate) rather than the sulfate form of potassium. Maintain soil micronutrient levels according to the results of a soil and foliar analysis. Keep soil pH between 5.8 and 6.2 and never apply high rates of lime, particularly to SDS-damaged bermudagrass. Instead, make incremental adjustments in soil pH by applying low rates of lime over time. Frequent core aerification will stimulate root growth and may suppress SDS-like diseases. Increasing mowing height, particularly on damaged greens, may reduce predisposing stresses, enhance rooting and accelerate recovery. Renovating summer patch-damaged Kentucky bluegrass turfs with disease-resistant cultivars or blends is an effective control. Since take-all damaged St. Augustinegrass rarely recovers, establishment of centipedegrass, zoysiagrass or bermudagrass may be the best control. While Floratam St. Augustinegrass may be partially resistant to take all root rot, Raleigh and Mercedes appear more susceptible. All seeded and vegetatively propagated bermudagrasses are susceptible to SDS.
Preventative fungicide treatments should be limited to turf previously damaged by a patch disease. Effectiveness of fungicides against some patch diseases is often erratic. To prevent further spread of bentgrass dead spot, summer patch, necrotic ring spot or bermudagrass decline, apply a curative treatments in the summer as symptoms appear. Depending on the fungicide, the best SDS control will be obtained with one or more late summer and/or early fall early treatments. Control of take-all root rot on St. Augustinegrass with preventative or curative fungicide treatments has never been conclusively demonstrated. Aerify before a fungicide is applied for patch-disease control and irrigate immediately to move the fungicide through the thatch to the roots.
Dollar spot is a common and often unsightly disease on most cool- and warm-season turfgrasses. While bermudagrass and zoysiagrass are main warm-season targets, damaging disease outbreaks may also be seen on centipedegrass and bahiagrass. Symptoms are usually seen on the above turfgrass in the summer; however, early spring and fall dollar spot outbreaks are not uncommon. Among cool-season turfgrass, bentgrass and fine fescue are most vulnerable to attack. Outbreaks are occasionally seen on Kentucky bluegrass and tall fescue. On cool-season turfgrass, dollar spot is strictly a mid- to late-summer disease. Nitrogen-starved turfs are most susceptible to dollar spot as are those stressed by hot, dry weather.
On closely mowed bermudagrass, zoysiagrass and bentgrass, dollar spot appears as circular tan-colored spots about 1 to 2 inches in diameter. On a green, collapse of the blighted turf will leave “pits” that will interfere with ball roll. On coarser lawn grasses such as centipedegrass or bahiagrass, patches may be less distinct but are larger compared with fine-leaf grasses. When left unchecked, spots coalesce to form large areas of blighted turf. On individual leaves, tan spots or bands with a dark brown margin appear. In the early morning, a network of fine fungal threads or mycelia may be seen suspended between the leaf spots on diseased leaves.
Cultivars of selected cool- and warm-season turfgrasses differ in their sensitivity to dollar spot. Among zoysiagrass selections, Emerald is more susceptible than El Toro, Belair or Meyer, while Korean is the least susceptible. In contrast, little difference in the sensitivity of seeded and vegetatively propagated bermudagrass to dollar spot has been noted. Tolerant or resistant bentgrass cultivars are L-93, A-1, Seaside, Seaside II, A-4, G-2, Providence, Pennlinks and the velvet bentgrass SR 7200, while Backspin, Century and Crenshaw are highly susceptible. Dollar spot-resistant Kentucky bluegrass cultivars include Moonlight, Sidekick, Award, Misty, America, Ascot, Odyssey, Total Eclipse, Quantum Leap, SR 2100 and Abbey.
On warm-season turfgrass, a light application of a fast release nitrogen fertilizer along with timely irrigation, which will speed the recovery of dollar spot-damaged lawns, fairways and greens, are often just as effective as fungicide treatments. For cool-season turfgrass, a little extra nitrogen fertilizer will help suppress dollar spot, but too much will increase the risk of Pythium blight and brown patch, particularly on bentgrass. Weekly deep watering when the weather is hot and dry, as well as higher summer mowing heights may also minimize dollar spot damage. Protective fungicide treatments are only necessary on highly visible lawns, greens or other turfs, particularly those with a history of this disease, where damage cannot be tolerated. Apply a recommended fungicide before disease onset is expected and retreat at the intervals on the label until the risk of disease has passed. Typically, a treatment program will run from June through August. Curative or therapeutic fungicide treatments may be made alone or in combination with a low rate of nitrogen to recently damaged turfs. Strains of the dollar spot fungus partially to highly resistant to bemimidiazole, dicarboximide and DMI fungicides are widely distributed. To avoid control failures due to resistance, alternating or tank mixing of two or more fungicides with different modes of action along with proper management is necessary. Preferably, one should be the broad spectrum, contact fungicide chlorothalonil or mancozeb. Note that chlorothalonil fungicides are no longer cleared for use on residential lawns.
GRAY LEAF SPOT
Gray leaf spot, which often damages St. Augustinegrass, has emerged as a devastating disease on perennial ryegrass and to a lesser extent on tall fescue. Steamy, hot mid- to late-summer weather and frequent showers favors rapid disease spread. Disease outbreaks are particularly destructive after a tropical storm. Excessive summer nitrogen fertilization and over watering increase turf susceptibility to gray leaf spot.
On warm- and cool-season turfgrasses, a purple to brown margin or halo surrounds the tan to light gray spots that often form often along the leaf mid-vein. Heavily spotted leaves yellow, wither and die. Irregular yellowed and thinned patches, which may be several feet in diameter, are associated with severe disease outbreaks on a warm- or cool-season turfgrass. From a distance, symptoms of gray leaf spot on perennial ryegrass could be confused with those of Drechslera (Helminthosporium) leaf spot or possibly rust.
Establishment of a disease-resistant turfgrass is an effective tool for controlling gray leaf spot. St. Augustinegrass cultivars Floratam, Delmar and Jade have good resistance but are restricted to the warmer parts of Florida and Texas due to poor cold tolerance. Tall fescue cultivars that are gray leaf spot resistant include Coronado, Coyote, Gazelle, Apache II, Durango and Vegas. Currently, gray leaf spot-resistant perennial ryegrass cultivars or blends are not available. Perennial ryegrass fairways and other turf destroyed by this disease may have to be replanted to Kentucky bluegrass, turf-type tall fescue, bentgrass or when conditions are less favorable for disease perennial ryegrass.
Frequent applications of low rates of fast release nitrogen fertilizers or using slow release nitrogen may lower turf vulnerability to gray leaf spot. For perennial ryegrass or tall fescue, apply enough nitrogen to maintain good color but not promote lush summer growth. When you see fresh damage, remove the clippings. Irrigating at a time of day so leaves will quickly dry.
Fungicide use should be limited to perennial ryegrass fairways and lawns that have a history of disease outbreaks. Treating sod fields is cost prohibitive. Begin making protective treatments before damage is seen in late spring or early summer. Repeat applications at recommended intervals until the threat of disease has passed. Always mow and irrigate before apply a fungicide. Due to the intensive fungicide program required to control gray leaf spot on perennial ryegrass fairways, there is a risk of control failure due to fungicide resistant strains of the causal fungus. Strobilurin fungicides azoxystrobin trifloxystrobin, and pyraclostrobin, as well as the benzimidiazole fungicide thiophanate-methyl have good activity against gray leaf spot but are at high risk for resistance-related control failures. Exclusive use of strobilurin fungicides on perennial ryegrass fairways has already resulted in the appearance of resistant strains of the causal fungus. To minimize the risk of resistance-related control failures, alternate or tank mix two or more several fungicides with different modes of action, as well as follow the resistance management guidelines on the label of strobilurin fungicides. On golf courses, chlorothalonil is a great tank-mix partner with an at-risk fungicide. Recommended fungicides are listed in the table on page 50.
LEAF SPOT AND CROWN ROT DISEASES
Leaf spot and crown rot diseases, which are caused by Bipolaris, Drechslera and Exserohilum (also called Helminthosporium) fungi, are reported on many cool- and some warm-season turfgrasses. Melting-out causes considerable damage to Kentucky bluegrass. Considerable stand thinning in turf-type tall fescues is attributed to net blotch. Leaf spot and crown rot are commonly seen on bermudagrass, particularly the seeded-types. Similar diseases are also occasionally seen on perennial ryegrass, bentgrass and zoysiagrass. While melting out on Kentucky bluegrass often appears in late April to early May, other leaf spot and crown rots are mainly mid- to late — summer diseases. Alternating periods of dry and wet weather favor disease outbreaks. Potash deficiency, excessive nitrogen fertility, phenoxy herbicide use, heavy shading and scalping susceptible cultivars increase disease severity.
Symptoms often appear as tiny purple to brown spots or streaks, especially on bermudagrass, zoysiagrass and tall fescue that are randomly scattered across the leaf surface. On Kentucky bluegrass, perennial ryegrass and sometimes bermudagrass, lens- to oval-shaped leaf spots with a tan center and a purple to brown border or halo are seen. Brown, irregular spots may also be found on the leaf sheaths of Kentucky bluegrass. As the disease intensifies, the diseased leaves turn yellow, wither and die. On badly damaged turfs, irregular patches of yellowed and thinning will be seen.
Establishment of disease resistant cultivars or blends is the best control for the above diseases. Overseeding damaged cool-season fairways and lawns with a disease-resistant cultivar or blend is an option. Some melting-out resistant Kentucky bluegrass cultivars are Admiral, America, Aspen, Baniff, Bono, Bristol, Challenger, Columbia, Eclipse, Midnight II, Somerset and Trenton. Leaf spot resistant perennial ryegrass cultivars include Manhattan II, Rebel, Birdie II, Cowboy, Derby, Diplomat, Gator and Regal. Rebel tall fescue appears particularly susceptible to net blotch. Tifway II bermudagrass is more resistant to leaf spot and crown rot than the seeded-cultivars Common, Sonesta, Cheyenne, Sundevil and Sahara.
Management practices listed under brown patch and gray leaf spot will reduce the risk of a damaging disease outbreak as well as accelerate turf recovery. In particular, maintaining a 1:1 to 2:1 nitrogen to potash ratio, removal of diseased clippings and thatch management are critical for leaf spot and crown rot control.
Limit fungicide use to highly visible turfs, particularly Kentucky bluegrass fairways that have previously been damaged by one of these diseases. Usually, following recommended management practices will be sufficient to suppress disease and promote lawn or fairway health. General guidelines for a preventative fungicide program are the same as those already described for gray leaf spot. Recovery of badly damaged turfs can be accelerated by combining a series of curative fungicide treatments and adjustments in fertilization practices.
OTHER TURFGRASS DISEASES
Other less common but damaging turfgrass diseases include leaf or stem rust on zoysiagrass, Kentucky bluegrass and perennial ryegrass; pink (Microdochium patch) and gray snow mold on bentgrass; Ophiosphaerella dead spot or “ball mark disease” on bentgrass; anthracnose on bentgrass, annual bluegrass and centipedegrass; copper spot on bentgrass; powdery mildew on Kentucky bluegrass; as well as red thread and pink patch on perennial ryegrass, tall and fine-leaf fescue and Kentucky bluegrass. Plant parasitic nematodes are especially damaging on bentgrass and bermudagrass tees and greens, particularly in the Southeast. Control practices for many of the above diseases are similar to those already described in this article. For more information, refer to the Web page of the land-grant university in your or an adjoining state for additional information concerning recommended fungicides, disease management practices and information concerning fungicide resistance. A lengthy discussion concerning fungicide resistance management can be found on the labels of dicarboximide, DMI, phenylamide and strobilurin fungicides, as well as the Fungicide Resistance Action Committee (FRAC) Web site at www.frac.com. Information concerning reaction of cultivars of warm- and cool-season turfgrass to diseases can also be found at land grant university Web sites, as well as at the National Turfgrass Evaluation Program Web site at www.ntep.org/contents2.shtml.
Austin Hagan is an alumni professor and extension plant pathologist at Auburn University (Auburn, Ala.).
|TURF FUNGICIDE||DISEASE CONTROLLED|
|CLASS||COMMON NAME||TRADE NAME*|
|anilide||boscalid||Emerald||Dollar spot, bentgrass dead spot|
|benimidiazole||thiophanate-methyl||Cleary's 3336, OPH 6672, Systec 1998, Cavalier, Fungo, Proturf Fluid Fungicide, T-Storm, Tee-Off||Anthracnose, bermudagrass decline, brown patch, copper spot, dollar spot, gray leaf spot, necrotic ring spot, pink snow mold, red thread, SDS, summer patch, take-all patch|
|benzanilide||flutolanil||ProStar||Brown patch, fairy ring, gray snow mold, pink patch, red thread, southern blight|
|carbamate||propamocarb||Banol||Pythium blight, summer decline|
|polyoxin D||Endorse||Anthracnose, brown patch, fairy ring, leaf spot and crown rot diseases, pink snow mold, red thread|
|dicarboximide||iprodione||Chipco GT, Chipco 26019, Sexton, Proturf Fungicide X, Iprodione Pro||Brown patch, dollar spot, leaf spot and crown rot diseases, necrotic ring spot, pink snow mold, red thread, yellow patch|
|vinclozolin||Curalan, Touche||Brown patch, dollar spot, gray pink patch, red thread, snow mold, pink snow mold|
|dithiocarbamate||mancozeb||Dithane T/O, 4 Flowable Mancozeb, Fore, Penncozeb, Protect T/O||Brown patch, leaf spot and crown rot diseases, rust|
|thiram||Thiram, Spotrete||Brown patch|
|DMI||fenarimol||Rubigan||Brown patch, copper spot, dollar spot, necrotic ring spot, pink snow mold, SDS, summer patch, take-all patch|
|myclobutanil||Eagle||Anthracnose, brown patch, copper spot, dollar spot, leaf spot and crown rot diseases, necrotic ring spot, pink snow mold, powdery mildew, rust, summer patch, yellow patch|
|propiconazole||Banner MAXX, Spectator, Propiconazole Pro, ProPensity||Anthracnose, brown patch, copper spot, dollar spot, gray leaf spot, gray snow mold, necrotic ring spot, pink patch, pink snow mold, powdery mildew, red thread, rust, SDS, stripe smut, summer patch, take-all patch, yellow patch|
|triadimefon||Bayleton T/O, Proturf Fungicide VII, Lesco Granular Turf Fungicide||Anthracnose, bermudagrass decline, brown patch, copper spot, dollar spot, gray leaf spot, gray snow mold, pink snow mold, powdery mildew, red thread, rust, stripe smut, summer patch, take-all patch, yellow patch|
|phosphonate||phosphate||Alude||Pythium blight, summer decline|
|phenylamide||mefenoxam||Subdue MAXX, Subdue 2G, Quell||Pythium blight, summer decline|
|phenylpyrrole||fludioxonil||Medallion||Anthracnose, bentgrass dead spot, brown patch, gray leaf spot, gray snow mold, leaf spot and crown rot diseases, pink snow mold, summer patch, yellow patch|
|phosphonate||fosety-AL||Aliette, Aliette Signature, Prodigy||Pythium blight, summer decline|
|strobilurin||azoxystrobin||Heritage||Anthracnose, brown patch, fairy ring, gray leaf spot, gray snow mold, leaf spot and crown rot diseases, necrotic ring spot, pink patch, pink snow mold, powdery mildew, red thread, rust, SDS, summer patch, take-all patch, Zoysia patch|
|pyraclostrobin||Insignia||Anthracnose, bentgrass dead spot, bermudagrass decline, brown patch, fairy ring, gray leaf spot, gray snow mold, leaf spot and crown rot diseases, pink patch, pink snow mold, powdery mildew, Pythium blight, red thread, rust, summer patch, take-all patch, yellow tuft|
|trifloxystrobin||Compass||Anthracnose, brown patch, gray leaf spot, leaf spot and crown rot diseases, pink patch, pink snow mold, red thread, rust, summer patch,|
|substituted aromatic||chlorothalonil||Daconil Ultrex, Daconil Weather Stik, Concorde, Echo, Manicur DG, Manicur Flowable||Anthracnose, brown patch, dollar spot, gray leaf spot, gray snow mold, leaf spot and crown rot diseases, red thread|
|PCNB||Defend 2F, Defend 10G, Revere 75W, Revere 400, Terraclor 10G, Turfcide 10G, Turfcide 400||Brown patch, dollar spot|
|*Many of the above fungicides sold as a mixture with a second fungicide as a prepackaged product using another trade name. Note — For a complete list of fungicides, see "Chemical Update" on page 34 in this issue of Grounds Maintenance.|
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