TURFGRASS DISEASES a triangular view of diagnosis and management

College of Agricultural Sciences Cooperative Extension

WHAT IS TURFGRASS DISEASE? Disease of sickness in turfgrasses, as in other plants, develops from an interaction 2. On the individual plant between a susceptible plant, a disease- SUSCEPTIBLE PLANT 1. On theSYMPTOMS stand producing organism (usually a fungus), and an environment favorable for the AMOUNT disease-causing organism to attack. The ENVIRONMENT AMOUNT OF sick turfgrass plant then gives visible OF DISEASE DISEASE evidence that something is wrong. This FAVORABLE ENVIRONMENT evidence of disease we call symptoms. during or just prior to disease onset This is the same situation that occurs in SIGNS OF THE CAUSAL ORGANISM human disease. For example, the disease- DISEASE-CAUSER (PATHOGEN) 1. Visible evidence causing streptococcal bacterium pro- 2. Microscopic evidence duces the symptoms (fever, sore throat, and rash) that physicians diagnose as the disease scarlet fever. Scientists who Figure 1. Disease triangle. Figure 2. Diagnosis triangle. work with turfgrass diseases sometimes use a disease triangle to illustrate the concept of disease. The three sides of the disease triangle represent three factors that interact to produce turfgrass disease: (Figure 2). The environment during the never appear as rings, while others always the disease-causer, the susceptible grass, onset of the disease is one source of diag- appear as rings. Symptoms to look for on and a favorable environment (Figure 1). nostic information. For example, what individual plants include leaf spots, leaf Three factors interact to cause turfgrass were the temperature, the light intensity, blight, wilt, stunt, yellowing, and root disease; therefore, and the moisture conditions just prior discoloration or rot. Leaf spots can be • we must observe all three factors to to and during disease development? The very good diagnostic clues because the gather information for diagnosis of nature of the disease site is also impor- leaf spots of different diseases are usually the problem, and tant. Air and water drainage, soil condi- unique in shape, color, and size. Leaf • we can change any or all of these tions, sun/shade, slope, and nearness of blighting can be any size or shape and three factors to combat the disease. other plantings or buildings all may be may involve the entire leaf. important in development of turfgrass Certain life stages of turfgrass THE IMPORTANCE OF diseases. Prior chemical applications to disease-causers can be seen without CORRECT DIAGNOSIS the site, including pesticides and fertil- magnification. The fungi that cause most The first step in turfgrass disease man- izers, may be contributive. Heavy thatch turfgrass diseases are microscopic. But agement is the identification of the accumulation and poor mowing practices in stripe smut, powdery mildew, and rust problem. Diseases are only one cause of that stress the turf may trigger or amplify diseases, the spores of the causal fungi turf loss, and disease control measures certain disease problems in turf areas. pile up in such numbers that they become will do nothing to alleviate damage from The nature of the symptoms on the visible as black, white, or orange powder other causes such as insect attack or grass is a very important source of diag- on grass leaves. In red thread disease, drought stress. It is essential to determine nostic information. Two kinds of symp- the fungus sticks together and forms the whether the problem is disease and, if toms should be looked for in diseased pink or red antlerlike threads that typify so, which disease it is. Disease manage- turgrass areas—symptoms on the stand the disease. When the causal fungus can ment strategies that are effective against and symptoms on individual plants. A be seen, its appearance is often the most one disease may have no effect on or home lawn, an athletic field, and a golf important clue for diagnosis. may even worsen another disease. This green or fairway are all examples of turf is particularly true when, because of stands. Symptoms on the stand are the incorrect diagnosis, the wrong fungicide appearance and the visible patterns of is selected. The best result that can be the disease on the planting. These are hoped for in this situation is that noth- extremely important in turfgrass disease ing is lost except time, effort, and money. diagnosis because different diseases A worse possibility is that the disease appear differently on turf stands. The problem may be increased by application visible differences in pattern are often of an inappropriate chemical. critical factors in identifying particular The three disease factors (grass, diseases. Diseases can appear on the turf disease-causer, and environment) provide stand as spots, patches, rings, circles, or the sources of information for diagnosis may be unpatterned. Certain diseases DISEASE MANAGEMENT disease. For example, certain varieties possible, to use mixtures of different ON TURFGRASS of Kentucky bluegrass are resistant to grasses or blends of different variet- spring leaf spot, a disease that is devas- ies rather than seeding a single kind of Beacause the three components of dis- tating on many Kentucky bluegrass turfs. grass. The seeding of mixtures or blends ease development combine to influence Varietal resistance to other common produces a diverse population of grass the onset on turfgrass disease, the task diseases of bluegrass is available. For plants. Such turf is usually more likely to of disease management on turfgrasses diseases to which varietal resistance is survive stress caused by disease. Diver- involves manipulation of these three— weak or not available, it may be possible sity in plantings almost always increases the environment, the grass, and/or the to seed a grass species that is resistant odds of survival. disease-causing organism—to favor to a prevalent disease problem. For The causal organism may be attacked the grass and inhibit the causal fungus example, ryegrass may replace bluegrass by applying chemicals that will either (Figure 3). in an area damaged by necrotic ring spot, kill the organism or keep it from grow- The environment can be altered in or bluegrass might replace ryegrass in an ing. Most fungicides do not actually kill many ways. The ones chosen depend area when Pythium blight is a problem. fungi; they work by preventing growth. on the disease to be managed. Water Disease severity can often be reduced Again, it is important to have identified manipulation can be a vaulable tool in by appropriate changes in the grass that the causal organism correctly so that an disease management. For example, some is being grown. It is a bad practice to appropriate fungicide can be selected. diseases require free water on leaves replant the same grass that has been Arbitrary selection and application of for development. Effective strategies to killed by the same disease year after year, fungicides without knowledge of the dis- reduce free water include morning irriga- if there is another option. ease cause can do as much harm as good. tion, removal of dew, and reduction in In selecting grasses for turf establish- Using the wrong fungicide wastes money amount and/or frequency of irrigation. ment or renvation, it is preferable, where and may increase the amount of disease Other management strategies may involve or produce other undesirable side effects. some forms of improved air and water With rising prices, declining budgets, drainage, improved soil conditions by and increasing environmental awareness, aeration, thatch reduction, manipulation those who manage turfgrasses are faced DISEASE-RESISTANT of light conditions, regulation of fertil- with the necessity of making reason- ization levels, and implementation of able and defensible choices. Planning an PLANT proper mowing practices. Environmental effective disease management program, modifications may be appropriate meth- therefore, involves not only “spraying ods for reducing damage from particular AMOUNT ENVIRONMENTALMODIFICATION OF something,” but selecting cost-effective diseases and ensuring a vigorous turf that DISEASE and environmentally sound disease recovers from disease injury. control strategies. The financial, envi- When establishing new turf areas or ronmental, and aesthetic costs of disease when renovating disease-damaged turf, FUNGICIDE APPLICATION management strategies must be consid- it is important to select grasses that are ered. Good, common-sense approaches resistant to diseases known to be com- to disease management should employ all mon in the area or that have damaged the available disease management strategies existing stand. Disease-resistant grasses (Figure 4). can be seeded to minimize turf loss from Figure 3. Management triangle.

+ DISEASE-RESISTANT+ = AMOUNT AMOUNT AMOUNT PLANT OF AMOUNT ENVIRONMENTAL OF DISEASE OF DISEASE DISEASE OF DISEASE MODIFICATION FUNGICIDE APPLICATION

Figure 4. Use all three management approaches to reduce the amount of turfgrass disease. DISEASE, DIAGNOSIS, AND MANAGEMENT TRIANGLES FOR SEVENTEEN COMMON DISEASES ON COOL-SEASON TURFGRASSES KBG = Kentucky bluegrass FF = Fine fescue PRG = Perennial ryegrass CrBG = Creeping bentgrass

DISEASE TRIANGLE DIAGNOSIS TRIANGLE MANAGEMENT TRIANGLE

blighted areas, grass bleached and matted

No resistant cool-season grasses; Plant symptoms: none important Stand symptoms: circular KBG and FF least susceptible All cool-season turfgrasses

GRAY GRAY GRAY

Avoid snow accumulations 30–40°F, high moisture, SNOW 30–40°F, high moisture, SNOW SNOW snow cover, lush growth snow cover, lush growth until grass growth ceases MOLD MOLD and late-fall fertilization; mow MOLD

Typhula spp. Fungal signs: small brown/black sclerotia Apply fungicides before permanent imbedded in infected leaves snow cover: chloroneb, fenarimol, iprodione, triadimefon

blighted areas, grass bleached and matted

No resistant cool-season grasses; Plant symptoms: none important Stand symptoms: circular KBG and FF least susceptible All cool-season turfgrasses

PINK PINK PINK

32–45°F,under high snow, moisture, cold rainSNOW MOLD, 32–45°F,under high snow, moisture, cold rainSNOW MOLD, SNOW MOLD,

Avoid spot accumulations of snow, FUSARIUM PATCH FUSARIUM PATCH mow until grassFUSARIUM growth ceases PATCH

leaves, mulch, and late-fall fertilization;

Fusarium nivale Fungal signs: grass may appear pink Apply fungicides before snow cover or when from accumulation of fungal spores disease is active: benomyl, fenarimol, iprodione, thiophanates, triadimefon, vinclozolin

Stand symptoms: small yellow CrBG on greens; PRG or KBG on fairways progressingPlant to symptoms: red; bases yellow of shoots leaves Replace annual bluegrass with

and leaf sheaths blackened to bronze patches

Annual bluegrass

50–60°F, wet 50–60°F, wet

Reduce soil compaction;

COLLETOTRICHUM COLLETOTRICHUM COLLETOTRICHUM BASAL ROT BASAL ROT increase soil aerification andBASAL drainage ROT

Colletotrichum graminicola Fungal signs: dark acervuli with black spines Combinations of chlorothalonil and benomyl (setae) on bases of shoots and leaf sheaths or triadimefon MAY reduce severity DISEASE TRIANGLE DIAGNOSIS TRIANGLE MANAGEMENT TRIANGLE

Bristol, Challenger,Resistant KBG: Eclipse, Birka, Enmundi, Bonnieblue, Stand symptoms: nonpatterned, Majectic, Parade, Ram 1, Touchdown; Plant symptoms: typical leaf spots substitute other grasses for KBG

red-brown appearance with red-brown margins Kentucky bluegrass

lush growth SPRING lush growth SPRING SPRING

50–65°F, high moisture, LEAF SPOT, 50–65°F, high moisture, LEAF SPOT, LEAF SPOT, MELTING OUT MELTING OUT MELTING OUT

benomyl, thiophanates, triadimefon Avoid early spring nitrogen, night watering,

Helminthosporium vagans Fungal signs: none present Apply fungicides on susceptible KBG when (Drechslera poae) leaf spots appear: anilazine, chlorothalonil, iprodione, maneb, vinclozolin

Plant symptoms: leaves yellowed or white

Stand symptoms: nonpatterned

Plant shade-tolerant KBG, Kentucky bluegrasses FF, or rough bluegrass are most susceptible

POWDERY POWDERY POWDERY 55–70°F, low light, 55–70°F, low light, poor air circulation poor air circulation MILDEW MILDEW increase air circulation MILDEW Prune trees to increase light;

Erysiphe graminis Fungal signs: leaves colored with Effective fungicides: benomyl, fenarimol, grayish-white mycelium or white spores propiconazole, thiophanates, triadmefon

Stand symptoms: nonpatterned

Plant symptoms: leaves yellow,

KBG most susceptible, but CrBG also affected shriveled, and shredded Plant resistant KBG; yellow and stunt substitute PRG or FF

STRIPE STRIPE STRIPE cool, wet weather cool, wet weather SMUT SMUT water to avoid drought SMUT Foliar symptoms appear in Foliar symptoms appear in Fertilize with balanced NPK;

Ustilago spp. Fungal signs: black sooty spore masses between Effective fungicides: fenarimol, leaf veins and rupturing through leaf epidermis propiconazole, triadmefon

Stand symptoms: nonpatterned No resistant plant material required Plant symptoms: none important Any ground-level surface,

including grasses

SLIME SLIME SLIME Cool, wet weather MOLD Cool, wet weather MOLD MOLD

No environmental modification required

Myxomycetes Fungal signs: leaves covered with blue, No fungicides required; remove spore masses blue-gray, or purple spore masses by mowing, brushing, or syringing DISEASE TRIANGLE DIAGNOSIS TRIANGLE MANAGEMENT TRIANGLE

water soaked when wet, white when dry KBG less susceptible than PRG and FF Bluegrasses, ryegrasses, fescues Plant symptoms:irregular leaves appearbleached patches Stand symptoms: appear white when dry

RED THREAD RED THREAD RED THREAD slow grass growth slow grass growth 60–75°F, high moisture, AND 60–75°F, high moisture, AND AND PINK PATCH PINK PATCH PINK PATCH avoid drought, avoid night watering

Maintain adequate nitrogen levels, irrigate to

Laetisaria fuciformis (red thread) Red thread signs: coral red strands Collect and destroy clippings; apply fungicides, Limonomyces roseipellis (pink patch) on and between infected leaves if necessary: anilazine, benomyl (red thread only), Pink patch signs: pink cottony growth chlorothalonil, iprodione, propiconazole, thiophanates on infected grass (red thread only), triadimefon, vinclozolin

on close-cutStand turf, symptoms: larger less-circular small circular areas areas on high-cut turf; bleached white when dry No resistant bentgrasses available; Plant symptoms: leaf spots bleached usually not a significant problem All cool-season turfgrasses; bentgrasses very susceptible on other cool-season grasses white; light-brown margins

DOLLAR DOLLAR DOLLAR SPOT SPOT SPOT

70–85°F, moisture on leaves, 70–85°F, moisture on leaves, Remove dew and guttation water from leaves, avoid night watering, maintain low soil moisture, low nitrogen levels low soil moisture, low nitrogen levels adequate soil moisture and nitrogen levels

Sclerotinia homoeocarpa Fungal signs: cottony white growth on Apply fungicides to protect susceptible grasses; anilazine, affected areas when moisture is present benomyl*, chlorothalonil, fenarimol, iprodione, propiconazole, thiophanates*, triadimefon*, vinclozolin (*Resistance has been a problem.)

rings of yellow, dark-green, or killed grass

Stand symptoms: various-sized Plant symptoms: none important

No resistant turfgrasses

All turfgrasses

FAIRY FAIRY FAIRY Any environment RING Any environment RING RING Limited and erratic success with soil removal and replacement, soil

cultivation and mixing, wetting agents and

watering; mask rings with applications of FE or N Basidiomycete spp. (mushroom fungi) Fungal signs: white fungal strands or cottony Limited and erratic successes with soil growth in the soil and/or thatch at fumigation and fungicide drenches the outer edge of rings

Parade, Ram 1, Touchdown. Resistant PRG: Diplomat, Manhattan, Omega, Player, Score, Eclipse, Enmundi, Majestic, Nassau, Plant symptoms: typical leaf spots with Sprinter, Yorktown II; resistantBonnieblue, FF: Biljart, Bristol, Challenger, Stand symptoms: nonpatterned, Centurion, Checker, Jamestown, Scaldis Resistant KBG: Birka,

All cool-season turfgrasses red-brown appearance

red-brown margins

SUMMER SUMMER SUMMER LEAF SPOT LEAF SPOT When disease is active, LEAF SPOT

80–90°F, high moisture, lush growth 80–90°F, high moisture, lush growth avoid applications of nitrogen, benomyl,

thiophanates, triadimefon, and night watering

Helminthosporium sorokinianum Fungal signs: none present Apply fungicides on susceptible grasses when (Drechslere sorokinianum) leaf spots appear: anilazine, chlorothalonil, iprodione, maneb/mancozeb, vinclozolin DISEASE TRIANGLE DIAGNOSIS TRIANGLE MANAGEMENT TRIANGLE

circles, “frog eyes” of wilted grass crescents, bluegrasses, and annual bluegrass Stand symptoms: KBG less susceptible than PRG and FF Major problem on KBG, but FF, Plant symptoms: roots and/or

that collapse and die may show symptoms steles dark brown

NECROTIC NECROTIC NECROTIC

Irrigate to prevent drought Root infection occurs during cool, RING SPOT Root infection occurs during cool, RING SPOT RING SPOT

wet weather; foliar symptoms appear wet weather; foliar symptoms appear stress; promote root growth by (1) during spring and fall when infected (1) during spring and fall when infected plants fail to make normal growth, or (2) plants fail to make normal growth, or (2)

during periods of heat and/or drought stress during periods of heat and/or drought stress vigorous aerification, balanced fall fertilizer

Leptoshaeria korrae Fungal signs: dark-brown to black fungal Begin preventive monthly fungicide applications threads on roots and crowns of infected plants when soil reaches 65°F: benomyl, fenarimol, iprodione, propiconazole

Stand symptoms: irregularly shaped,

Most bentgrasses are susceptible; Plant symptoms: foliage bronzed; use other grasses where possible Major problem on bentgrasses roots and/or stelescircular, dark bronzedbrown patches

TAKE-ALL TAKE-ALL TAKE-ALL PATCH PATCH Avoid lime and alkaline PATCH Root infection occurs during cool, Root infection occurs during cool,

wet weather; foliar symptoms appear wet weather; foliar symptoms appear fertilizers;of sulfurlower orpH acidifying by applications fertilizers (1) during spring and fall when infected (1) during spring and fall when infected plants fail to make normal growth, or (2) plants fail to make normal growth, or (2)

during periods of heat and/or drought stress during periods of heat and/or drought stress

Gaeumannomyces graminis Fungal signs: dark-brown to black fungal Spring and fall applications of fenarimol, threads on roots and crowns or infected plants propiconazole, or triadimefon may provide symptom supression

of yellowing annual bluegrass; bentgrass Stand symptoms: circular patches Encourage bentgrass or PRG in affected areas

Plant symptoms: roots and/or steles Major problem on annual bluegrass unaffected in mixed stands

dark brown

SUMMER SUMMER Avoid overwatering; SUMMER PATCH PATCH PATCH

85–95°F, high soil moisture 85–95°F, high soil moisture promote surface and subsurface drainage; promote root growth by

vigorous aerification, balanced fall fertilizer

Magnaporthe poae Fungal signs: dark-brown to black fungal threads Begin preventive monthly fungicide applications on roots and crowns of affected plants when soil reaches 65°F: benomyl, fenarimol, propiconazole, triadimefon

Plant symptoms: water-soaked blight on leaves

edge ofsometimes circle;blighted blighted with areas areasa “smoke on may close-cut ring”be at turf, PRG and bentgrasses most susceptible Stand symptoms: circular

irregular shape on high-cut turf KBG and FF least susceptible No resisant turfgrasses;

BROWN BROWN BROWN PATCH PATCH PATCH (RHIZOCTONIA (RHIZOCTONIA Remove dew and guttation water(RHIZOCTONIA BLIGHT) BLIGHT) from foliage; avoid night watering in hotBLIGHT) 80–90°F, high soil moisture, lush growth 80–90°F, high soil moisture, lush growth weather; keep nitrogen levels low to moderate

Rhizoctonia solani Fungal signs: white, cottony growth on Apply fungicides on susceptible grasses: affected areas when moisture is present anilazine, benomyl, chlorothalonil, fenarimol, flutolanil, iprodione, maneb/mancozeb, propiconazole, thiophanates, tridimefon, vinclozolin DISEASE TRIANGLE DIAGNOSIS TRIANGLE MANAGEMENT TRIANGLE

Plant symptoms: water-soaked blight on leaves areas mayStand occur symptoms: where water nonpatterned runs or stands blighted

PRG and bentgrasses most susceptible

KBG and FF least susceptible No resistant turfgrasses;

PYTHIUM PYTHIUM PYTHIUM BLIGHT BLIGHT BLIGHT Improve soil drainage and air

85–95°F, high moisture, lush growth 85–95°F, high moisture, lush growth movement; avoid night watering in hot

weather; keep nitrogen levels low to moderate Pythium aphanidermatum Fungal signs: white cottony growth on affected Apply fungicide at first sight of disease: chloroneb, areas when moisture is present etradiazole, matalaxyl*, phosethyl chloroneb, propamocarb (*Resistance has been a problem.)

Stand symptoms: nonpatterned yellowing

KBG most susceptible; PRG also affected Plant resistant KBG; substitute PRG or FF Plant symptoms: leaves yellowed

around pustules

RUSTS RUSTS RUSTS

water to avoid drought Fertilize with balanced NPK; Slowly growing grass from low Slowly growing grass from low

fertility, drought, or low temperature fertility, drought, or low temperature

Puccinia spp. Fungal signs: pustules on leaves with Effective fungicides: fenarimol, maneb fungicides, rust-colored spore masses propiconazole, triadimefon

Prepared by Patricia L. Sanders, associate professor of plant pathology.

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