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• LAWN DISEASES 5 Sfungus Drechslera poae and leaf borne spores. The spores function spot by the fungus Bipolaris like seeds, producing new infections sorokiniana. Excess thatch, heavy whenever the environment is nitrogen fertilization, excess shade, Fusarium Blight favorable for a period of time and the mowing too close, and broad leaf - host is susceptible. Disease develops herbicides promote these diseases. The disease formly called when the pathogen (fungus) is The melting out pathogen, D. poae, "Fusarium Blight" or "Fusarium present on a susceptible host can also cause leaf spots. Conversely, Blight syndrome" was once thought (bluegrass) in a favorable environment the leaf spot pathogen, B. to be a distinct disease characterized (temperature, moisture/water, light, sorokiniana, can also causing melting by patches of grass that develop nutrients, and stress factors). out symptoms. "frog-eye" patterns. These consist of Lawn diseases are not always easy Leaf spot occurs in warm weather donut-or crescent-shaped areas of to diagnose. Some key factors and and is easily recognized. Spots on the dead or dying grass with a center of symptoms to help recognize disease leaves develop purplish-red to green grass. Now this disease is recognized to be a complex of rather include: size and shape of dead and purplish-brown borders and brown to similar appearing diseases that dying plants, specific spots on leaves, tan centers (figure 1). The spots may include Necrotic Ring Spot, quality of root system, leaf color and extend the width of the leaf and are Rhizoctonia Yellow Patch, and growth characteristics, time of year, somewhat longer than wide. Leaf Summer Patch (figure 3). and temperature when disease spots may cause the death of leaf developed. When diagnosing a lawn tips. Leaf sheaths are also infected, disease it is helpful to have a record and may die, resulting in thin stands of treatments such as ferti I izer, of grass. Melting out begins as spots herbicides, mowing height and on the leaf blades and rapidly moves frequency, watering .frequency and down the leaf sheath and into crowns amounts. and roots. I n advanced stages, when Grass disease can ruin a lawn's many plants die in a large irregular appearance. However, good turf patch, it is known as "melting out" management practices usually are (figure 2). These patches may range in II adequate to prevent serious damage. size from several inches up to many • Necrotic Ring Spot Integrated cultural practices for turf feet and may produce an irregular management and pest control will patchwork across an entire lawn. This is a serious disease of limit the need for fungicides. Disease Once established, melting out is Kentucky bluegrass that is especially development often is associated with difficult to control. Proper watering common on high maintenance lawns. the lack of proper appl ication of these and fertilization for bluegrass Necrotic Ring Spot is caused by t urf management practices: 1) varieties in your lawn will reduce the Leptosphaeria korrae, a fungus which selection and planti ng of an adapted danger of melting out. Common is most active in spring and fall, grass variety, 2) sufficient water at the Kentucky bluegrass should not be although symptoms may be observed correct time, 3) timely fertilization fertilized as heavily as the elite throughout the season. Initial with the right amounts and balanced bluegrass varieties or high symptoms are patches 6-24 inches in nutrients, 4) regular mowing at the maintenance diseases will develop. It diameter with a mixture of normal, recommended heignt, 5) provision for is particularly important to avoid straw- and red-colored blades around adequate sunlight and air movement, excess use of nitrogen fertilizer and the outer portion of the ring, resulting 6) maintenance of good soil aeration evening watering. Remove excess in a "frog-eye" pattern. The roots and and drainage, and 7) thatch thatch - the layer of plant material crowns of affected plants are covered management. tightly interwoven with I iving tissue with black strands of the Necrotic between the soil surface and the Ring Spot fungus. Thatch may green vegetation. Fungicides may be decompose in the patch areas, giving needed to control leaf spot disease. them a sunken or depressed Thei r effect is temporary and appearance (figure 4). I n warm beneficial only when combined with a weather, the red blades are seldom change in cultural practices. seen. Plants affected in the cooler Fungicides are most effective if the weather of spring and fall are initial application is made when leaf weakened and very susceptibl e to spot first becomes serJous and less summer heat and drought stress. This effective when small patches of lawn stress may lead to the death of begin to die. When large areas of a weakened plants and an apparent lawn are dying or dead from melting resurgence of symptoms, even thoug• out, dead patches should be reseeded the fungus may not be active at this with a resistant variety. Bluegrass time.

2 Once Necrotic Ring Spot is irrigation or an absence of irrigation established, it is difficult to control II during hot weather may make the _ d damage may remain or reappear disease more severe. arly for 2-4 years. Control requires a Rhizoctonia Yellow ombination of management practices including: thatch control, Patch adjustment of ferti lizer practices, Rhizoctonia Yellow Patch is also a reli eving soil compaction, changing serious disease of Kentucky watering practices, and possible use bluegrass. It is caused by the fungus II of a fun gicide. Rhizoctonia cerealis and is favored by Thatch should be kept less than 1/2 cool, wet weather. Since excessively Sclerotinia Dollar Spot inch thick. Vertical mowing or power wet conditions favor Rhizoctonia Dollar Spot, caused by the fungi raking should be done in spring or fall Yellow Patch, it frequently damages Lanzia spp. and Moel/erodiscus spp., to reduce thatch. The power rake new sod laid on heavy soils and it produces 2-3 inch circular patches on blades should be set to penetrate the may occur in lawns with heavy thatch creeping bentgrass turf and 4-6 inch thatch to the soil. Lawn mower and compacted soils. circular to blotchy areas on bluegrass attachments are less effective in Early symptoms are 2-3 inch lawns. These patches are straw thatch removal. It may take several patches of light green to yellow green colored ('figure 6). Early in the years for vertical mowi ng to effect grass. These areas soon turn light tan morning, when the grass is covered sufficient thatch removal. Top or brown and may increase up to 2 with dew, a faint cobwebby growth dressing, that is, spreading a thin feet in size. A "frog-eye" symptom is may be seen on the leaves of affected layer of soil on the grass, is another common, with yellow-green to brown plants (figure 7). I n the early stages of means to speed thatch breakdown. An grass surrounding green centers disease, leaves develop distinct tan­ aerator can also be used to remove a (figure 5). The patches may have a colored spots and bands; quite often core of thatch and soil. The soil when sunken appearance due to thatch a reddish-brown border can be seen deposited on the surface, wi II aid decomposition. Leaf blades near the on the leaf spots. thatch breakdown. Aeration also margin of the patch may have a Dollar Spot develops at reduces soil compaction, improves reddish to reddish-purple tint, water penetration, and stimulates root temperatures of 60°-85° F wi th high beginning at the leaf tip and humidity and low soil moisture. The development. I n areas where sod of continuing downward. Tan spots with one soi I type is placed on soi I of disease usually develops on lawns dark borders may develop on the which are unfertilized but anothe r type (for example, peat sod blades prior to complete bl ighting. on heavy clay), shal low roots often occasionally occurs on high The symptoms and the time of year of maintenance lawns under stress. It develop. Aerat ion w ill help alleviate occurrence overlap with Necrotic Ring is pro ble m. Reducing thatch by any can be controlled by keeping lawns Spot. The roots and crowns of adequately fertilized and watered and these methods will help reduce Rhizoctonia Yellow Patch diseased ummer drought stress. by using a fungicide as necessary. turf do not have black strands of Bluegrass varieties differ in Dollar Fertil izer practices need to be fungus on them. Spot susceptibility with most be ing adjusted . Avoid excessive use of Cultural controls discussed under moderately susceptible or moderately nitrogen fertilizer in the spring. One Necrotic Ring Spot can be used on resistant. pound of actual nitrogen per 1,000 Rhizoctonia Yellow Patch. Particular square feet can be applied in early emphaSis should be placed on September, and another when the reducing wet conditions and providing grass goes dormant after the last aeration where sod is laid on heavy mowi ng (late October to early soils. No fungicides are effective for November). Use a I ight application (112 control of Yellow Patch. pound of nitrogen) in the spring and summer only if it is needed to keep II the grass growi ng. Rhizoctonia Blight Watering practices must be changed. Use freq uent light (Formerly Brow n Patch) waterings, to keep the top 1/2 -2 in ches II Rhizoctonia Blight is a hot weather moist. Irrigation is critical during the disease. The fungus, Rhizoctonia summer heat, as the water applied Summer Patch solani, produces roughly circular during the day will help relieve both Summer Patch, caused by the patches on lawns. These patches are heat and drought stress. fungus Magnaporthe poae, is less 1-3 feet in diameter. In humid Fungicides may also assist in common on Kentucky bluegrass. It is weather, the outer edge of each patch control, if applied before damage is a disease that occurs during the hot may have a dark gray to dark purple too severe. Dead patches may be portion of the summer. The initial ring early in the morning while the reseeded using a resistan t bluegrass symptoms are yellow patches 6-12 grass is sti II covered with dew. This variety or ryegrass suitable for lawns. inches in diameter. The turf in these diagnostiC symptom, called a "smoke Resodding is usually not effective and patches thins and the remaining turf ring," disappears later in the day. At the disease m~y reappear quickly. turns bronze in color. If warm weather first the grass has a dark, water­ continues, all of the turf in the patch soaked appearance but soon dries out may die. The dead patches may be to a light brown (figure 8). colonized by weedy grasses. The Rhizoctonia Blight fungus is Soil moisture is important in most active at 80 o -gO°F temperatures • disease development. Excess when grass leaves stay wet for a long 3 Figure 4. Decomposition of thatch in Figure 8. Rhizoctonia blight produces patch affected turf resulting in roughly circular patches of discolored sunken or depressed areas. (WCS) turf one to three feet in diameter. (WCS)

Figure 1. Purple to brown spots with lighter centers develop on leaves and leaf sheaths infected with leaf spot/melting out fungi. (RWS) Figure 5. Rings of yellow to brown grass surrounding green grass. This Figure 9. Powdery mildew produces a "frog-eye" symptom is characteristic white powder-like growth on the of Rhizoctonia yellow patch. (POL) leaves of infected turf. (POL)

Figure 2. Thinning out of the turf occurs when crowns are killed by leaf Figure 6. Light colored blotchy areas Figure 10. Circular patches of spot/melting out fungi. (WCS) of bluegrass turf infected by the fungi diseased turf coalesce to form larger which cause dollar spot. (CLA) areas of turf affected by Typhula blight. (MCS)

Figure 3. Donut or crescent shaped Figure 7. Cobwebby growth visible areas of dead or dying grass are early in the morning when dew is Figure 11. Rust on turf is identified symptomatic of the patch disease present on dollar spot affected turf. by the orange pustules that break complex. (WCS) (WCS) through the leaf surface. (RWS)

4 (figure 9). In dense shade, Powdery Mildew causes the affected areas of leaves to turn yellow, eventually resulting in the yellowing and dying of lower leaves or even in the death of plants. Powdery Mildew develops in areas of dense shrubbery or trees where there is poor air circulation, considerable shade, and high j humidity. It is favored by temperatures of 60°-72°F. In many Figure 15. Inner and outer zones of cases, Powdery Mildew can be stimulation, and zone of inhibition in controlled by selective pruning of turfgrass caused by fairy ring fungi. shrubs to allow better air circulation (CLA) and greater penetration of sunlight. Where Powdery Mildew is a problem, avoid susceptible grass varieties or plant alternate ground covers.

Figure 12. Shreading of leaf blades II by the stripe smut fungus. (RWS) Typhula Blight (Formerly Gray Snow Mold) The snow molds usually appear in Figure 16. White to gray slime mold the spring as the snow melts from on bluegrass turf. (WCS) lawns (figure 10). There are two common types of snow mold: Typhula Blight and Fusarium Patch.They usually can be distinguished by their symptoms; develop under slightly different conditions; and are controlled by different fungicides. time. It is most severe when excess Typhula Blight is caused by the low­ nitrogen fertilizer has been used. A temperature fungi, Typhula incarnata night temperature above 70°F and a and T. ishikariensis, especially active long dew period favors rapid under the snow covering unfrozen Rhizoctonia Blight development. ground. Typhula Blight damage first The danger of Rhizoctonia Blight is appears when the snow is melting. Figure 13. Bright red threadlike reduced by following recommended strands of the red thread fungus form management practices, particularly by Roughly circular patches 2 to 40 near the tips or cut surfaces of the avoiding excessive use of nitrogen inches or more in diameter develop. leaf blade. (POL) before hot weather and avoiding These patches are straw COlored, and enlarge as long as the grass remains excessive thatch buildup. When cold and wet from melting snow. The weather favors this disease, a grass in the patches has a matted fungicide may be needed. appearance, and may have a visible gray colored mold growth on the whole patch or on the advancing margin. Hard fungus bodies called sclerotia develop on or are imbedded in the leaves and crowns of affected plants. These sclerotia are more or II less spherical in shape. The sclerotia of T. ishikariensis are the size of a Powdery Mildew pinhead and black; those of T. incarnata are up to 3/16 of an inch in Powdery Mildew is a common diameter and brown. These sclerotia's problem on bluegrass lawns in shady presence help diagnose Typhula areas. The mildew fungus, Erysiphe Blight. graminis, attacks the surface of the grass leaves, developing a fine, fungal The Typhula fungi survive the Figure 14. Watersoaked appearance growth that resembles a white summer in the soil or thatch as of Pythium blighted turf. (WCS) powdery substance on the leaves sclerotia. Active growth of the fungus

5 resumes in the absence of light under 15) wi ll not promote lush growth and remove the cl ippings, an important snow cover on un froze n ground. snow mold. Snow molds do not occur source of the rust fungus. Fungicides Growth takes place at temperatures often enough on lawns to merit a fall are not usually needed or economical • .. as low as freezing (to slight ly below application of fungicide as a for homeowners, but may be required freezing) and continues after snow preven tive measure unless there is a to help protect new growth when rust melt in the spring for as long as the history of snow mold. When snow is severe and weather promotes rust grass remai ns wet and the mold is observed in the spring it is development. temperatures cold. Typhula activ ity usually too late to apply fungicide. stops when the temperature exceeds Typhula Blight normally continues 45° F or the surface is dry. development for only a few days after Man agement practices fo r control the snow is gone. Fusarium Patch can of Typhu la Blight are similar to th ose develop longer, following snow melt, for Fusarium Patch. Fungicides are especially when cold rain or late II seldom needed in bluegrass lawns. spring snow is expected. The application of a fungicide might Stripe Smut prevent add itional damage from Stripe Smut, caused by the fungus Fusarium Patch but is se ldom Ustilago striiformis, is a cool weather recommen ded. disease that sometimes shows up during long periods of cool weather in II spring or fall. It is favored by extended periods of 50 0 -60 0 F Fusarium Patch weather. No symptoms develop wh en summer temperatures are 90°F for (Formerly Pink Snow II long periods. Mold) Rust Lawns with Stripe Smut exhibit poor growth and often are patchy, The Fusarium Patch fu ngus, Ru st, caused by Puccinia spp., is Microdochium nivalis, produces uneven, and thin. Leaves on infected not seen every year, but sometimes plants develop elongated streaks that yellowish patches from several inches becomes severe on susceptible to a foot in diameter which usually are yellow-green, later turn gray, then varieties during hot periods of the finally black. When the streaks turn appear as soon as the snow begins to sum mer when grass growth is melt and continue to enlarge as long black, the leaf surface is broken an d a reduced. When rust is severe, the black powder (s pores of the smut as the weather is cool and the grass lawn may have a yellowish to reddish­ wet. The patches soon take on a fungus) is liberated from the black orange appearance. A red-oran ge dust streaks (figure 12). This lengthwise bleached appearance. When the grass fills the air when the grass is mowed remains wet, it may be covered by a rupturing spli ts the leaves lengthwise and also collects on shoes and into narro w strips or ri bbons. The tip mat of cottony mold which is off­ clothing. Individual blades of grass white or faint pin k. Th is pink color of these strips curl downward; the will have slightly elongated yellow­ leave s turn brown and die. Infected and the absence of sclerotia orange to red-orange spots or distinguish Fusarium Patch from plants may be killed, resulting in th in pustule s (filled with a rusty colored stands of grass. Typhula Blight. Usually only the powder - the spores of the rust leaves of Kentucky bluegrass are fungus) that break th rough the leaf Stripe Smut attacks some varieties killed but entire plants may be killed surface (figure 11). When rust is of bluegrass, as well as creeping in years of severe snow mold activity. severe, the grass blades turn yellow, bentgrass. Control is seldom re qui red Fusarium Patch develops under a wither and die. Rust may also weaken since the disease is rarely severe. snow cover on unfrozen ground and a lawn, making it more susceptible to Where damage is occurring, an also can develop in cool wet weather winter kill the following winter. application of nitrogen and deep in fall and spring as long as the Rust is favored by hu mid weat her wateri ng early in the day will temperature is between 32° and 60°F. with night temperatures of 70 °-75° F, sti mulate growth and aid re covery. The two snow mold diseases do not day temperatures of 85°-95°F, Avoid frequent light watering in late occur every year on lawns, but are wetness from dew lasting many hours afternoon or evening, as th is may most apt to occur in a year when an after sunrise, and freq uent light rai n promote disease development. If early and deep snow cover prevents (or watering). Rust may be especially disease is severe, the fungicide the ground from freezing. A cold open severe on Merion and Touchdown benomyl may be used in late fall or winter will not promote snow mold on varieties of bluegrass, which are early spring. lawns but may cause winter injury, highly susceptible. When weather with patches of grass dying because favors rust, the disease is more likely the crowns were kill ed by freezing to be severe on low maintenance and/or drying (des iccation). lawns - lawns with low soil fertility Proper lawn management will and some degree of drought stress. It reduce the danger of snow molds. is also apt to be a problem in shady II Management practices in clude areas, on closely cu t grass, and on keepi ng the lawn mowed in the fall so newly laid sod. Red Thread that there is no thick mat of grass for Rust is easily controlled by Red Thread, cau sed by the fungus the snow molds to develop on. Lawn maintaining good lawn growth with Laetisaria fuciformis, is favored by areas where snow molds occur adequate fertilization and ad equate cool, hum id weather. Red Thread may should not be heavily fertilized in late watering. Once normal growth is become more common on lawns with summer or early fall. A late fall obtained, mow the grass freq uently at fescue and ryeg rass blends. Red application of fertilize r (after October recommended mowing heights an d Thread cau se s the lawn to have a

6 yellowing and weakening of the grass, the applicator technique. Spi lls of lawn a grayish cast. Mowing grass so making it more easily attacked by products such as oil, gas, and short that yellow or brown tissue is other organisms. The simplest control cleaners usually result in severe, long exposed is called scalping. This may of Slime Molds is to brush them off lasting dead patches. It is often result from a wheel dropping into a the grass with a broom or rake. necessary to know what was done on depression or from infrequent the turf area to correctly diagnose the mowing. Grass can die after being damage. If the spilled product is scalped. Some recovery does occur quickly removed and/or washed away from underground stems and some damage can be prevented. rhizomes if scalping is not repeated. II Some products can be inactivated Grass can wear out and die from with absorbent materials such as excessive use: such as base areas Moss and Algae activated charcoal. from softball games, the front line of Moss and algae are primitive green Physical agents (temperature, water a volley ball game, or push-off areas plants often found in densely shaded and ice, soil compaction, buried under swings. If the activity did not and moist lawn areas and sometimes objects, and thatch) can damage turf. remove the grass crown, recovery can on landscape materials and buildings. So can high or low temperatures. be expected. Rotate activity zones The best control involves improving Winter kill may be direct from ice and aerify soils to prevent damage soil drainage, increasing air crystals forming in cells or indirect and encourage plant regrowth. circulation and light intensity, and (dehydration) when unfrozen plants planting shade-tolerant ground covers are in frozen soil. Hot objects like or turfgrass varieties. Chemical engine exhaust or containers of hot controls for algae are available but liquids placed even for a short period are only a temporary solution and may on live grass will kill plants. Even cause injury to adjacent vegetation. solar radiation and lightning strikes can kill grass. Water extremes cause many turf problems and cannot always be separated from temperature effects. Lack of water obviously restricts plant growth and makes plants more susceptible to damage. II Water deficiency symptoms are greater next to sidewalks, driveways Dog Damage and buildings, on sloped areas or in Grass may be injured by dog urine. shallow soil. Soils can become The spots resemble Dollar Spot or impervious to water due to Rhizoctonia Blight. The difference is compaction or biological activity that outside the area of dead grass (referred to as a local ized dry spot). there is often a zone of grass with An excess of water, either flooding or luxuriant growth. Heavy watering will saturation of soils, creates conditions wash down excess salts and help the for poor root growth and results in grass recover. weakened or dead turf. Ice layers can cause turf suffocation. Thatch, the layer of plant litter on the soil surface, can reduce movement of water, air, and nutrients into the soil and restrict movement of gases out of Photo credits the soil. Roots growing in a thatch II layer are at high risk to drought, high CLA - C.L. Ash temperature damage, and disease. POL - P.O. Larsen Abiotic (Non-Living) MCS - M.C. Shurtleff Mechanical agents (mower injury, Agents of Disease scalping, and abrasion) also have RWS - R.W. Smiley negative effects on turf. A dull mower WCS - W.C. Stienstra Chemical agents (pesticides, salts, blade does not cut the leaf cleanly. fertilizers, and fuel or oil) can cause Leaf shredding, common with dull direct damage. Materials applied to rotary mowers, causes the leaf tip to turf for a purpose, such as ferti I izer or Cover Photo: Patch disease turn brown and die. The injury can symptoms in a lawn. Note the circular herbicides, usually produce damage assist disease entry and gives the in a pattern that repeats or follows pattern and sunken appearance. (POL)

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