Turfgrasses planted in North Carolina are prone to many diseases. Accurate diagnosis of a disease is the most important step in managing it. Fortunately, there are only about seven diseases that can develop in cool-season turfgrasses used in the landscape each year. This publication emphasizes diagnoses of these common turfgrass diseases and the use of cultural practices to help prevent severe damage. See also "Additional Resources" for more information on identifying, preventing, and managing fungal diseases, including laboratory testing.

Three factors are required for a disease to develop: a susceptible plant, a pathogen, and an environment that is favorable for pathogen growth. Disease will not develop unless all of these factors are present for several consecutive days. Because turfgrasses are perennial, the host plant is always present. The pathogens are always present as well, lying dormant in the thatch and soil when they are not causing disease. Therefore, it is the environment that triggers disease development. Weather conditions, management practices, and microclimate (for example, conditions that are specific to a particular location, sun or shade exposure, or air flow) are the variables that have the greatest impact on disease development.

Turfgrasses are most susceptible to disease when they are stressed or growing slowly. As a result, the most severe disease problems on cool-season grasses occur during the summer. Selecting a turfgrass that is well adapted for the location and its intended use will drastically minimize disease problems. Management practices also have a major impact on disease development. Grasses that are healthy and vigorously growing are far more tolerant of disease than grass that is poorly managed. Furthermore, healthy turf will also recover more quickly should disease develop.

The vast majority of turfgrass diseases are caused by fungi. Most fungi cause foliar diseases by attacking the leaves of the turfgrass. Others specifically attack the crowns or roots of turfgrass plants. Most fungi grow only within a specific temperature range and also require ample moisture. Foliar diseases typically thrive when the turfgrass leaves are wet from dew and during the cooler temperatures that occur at night. For example, brown patch may develop when low night temperatures exceed 60°F (16°C) for several consecutive days. Crown and root diseases are most strongly affected by conditions in the soil, such as temperature, pH, drainage, and compaction.

Fungicides can be used to control turfgrass diseases. Fungicides may be either preventive, if applied before symptoms of the disease appear, or curative, if applied after symptoms appear. Preventive fungicide programs are recommended for diseases that occur annually, such as brown patch in tall fescue. Curative fungicide applications are less effective and usually require increased application rates or shorter application intervals. Whenever possible, schedule preventive fungicide applications based on the existing weather conditions that favor disease development, not based on the calendar.

Fungicides can be grouped into two categories: contact and systemic. Contact fungicides remain on the leaf surface after application, forming a protective barrier against fungal infection. Contact fungicides protect only the plant parts that are sprayed; therefore, uniform applications are necessary to ensure complete protection of the turf. Contact fungicides must also be reapplied frequently because they are removed from the leaf surface by mowing, precipitation, irrigation, and traffic. In contrast, systemic fungicides are absorbed by the plant and translocated. Most systemics are translocated only upward in the plant. Because systemic fungicides are absorbed by the plant, they are longer lasting and are more effective than contact fungicides for curative applications. In general, systemic fungicides have a more limited control spectrum; therefore, you must accurately identify a disease to select the best fungicide for its control.

Some fungicides may lose effectiveness due to the development of resistance. Fungicide resistance occurs when fungicides from the same chemical class are applied repeatedly. Repeated applications allow strains of the pathogen that are naturally resistant to the fungicide to build up in the population. When resistant strains become dominant in the population, the fungicide no longer controls the disease, and significant damage may occur when conditions become favorable for disease development. Certain diseases, such as dollar spot and gray leaf spot, develop fungicide resistance quickly, after as few as five consecutive applications. Brown patch, however, has little risk for resistance development and there are no documented cases of control failures due to fungicide resistance. To prevent the development of fungicide resistance: (1) use integrated pest management (IPM), including selection of appropriate species and variety, and good cultural management practices; (2) rotate to a different class of fungicides after every application; and (3) tank-mix systemic fungicides with a contact fungicide, which will suppress resistant strains and slow their emergence.

Pathogen — Multiple species of Rhizoctonia (fungus)

Hosts — Bentgrasses, fescues, and ryegrasses

Overview

Brown patch is a fungal disease of cool-season turfgrasses. In higher cut turfgrasses (greater than 1 inch), symptoms are usually circular patches that are brown, tan, or yellow in color and range from 6 inches to several feet in diameter. The affected leaves have unique, tan lesions, irregular shape, and often a dark brown border.

Brown patch is most severe during extended periods of hot, humid weather. Brown patch will become active when night temperatures exceed 60°F (16°C) but will be most severe when temperatures are above 70°F (21°C) at night and 90°F (32°C) during the day. Poor drainage, lack of air movement, shade, prolonged cloudy weather, dew, overwatering, and watering late in the afternoon all favor prolonged leaf wetness, which increases brown patch severity.

Cultural Control

Turfgrass varieties of the same species can vary widely in their susceptibility to brown patch, therefore it is a best management practice to plant varieties with improved brown patch resistance.

Overfertilization can increase the severity of brown patch. In general, cool-season turfgrasses should receive no more than 1 lb nitrogen/1,000 square feet at any one time. Do not apply more than 0.5 lb nitrogen/1,000 square feet when conditions favor disease development. If applications are kept at or below 0.5 lb nitrogen/1,000 square feet during this time, they will not increase brown patch severity. As always, be sure adequate amounts of phosphorus, potassium, and other nutrients are applied (based on soil test results).

Reducing leaf wetness will greatly reduce brown patch severity. Leaves can become wet from irrigation, rain, dew, or guttation (water exuded from turfgrass leaves during the night). Do not irrigate daily. Instead, irrigate based on weather conditions and the water requirements of the turf. The time of day for irrigation is also critical; it is best to irrigate early in the morning, just before sunrise. This removes large droplets of dew and water from the leaves and speeds drying of the foliage after sunrise. Avoid watering after sunrise or in the late afternoon or evening, as this will increase the duration of leaf wetness.

Proper landscape design and site preparation can help to minimize brown patch. Turf surrounded by trees, shrubs, buildings, or other barriers will remain wet for extended periods due to reduced air movement and less sunlight. Removal or pruning of trees and other barriers will help minimize leaf wetness and discourage brown patch development.

Chemical Control

Fungicides are effective for brown patch control and can be used as a preventive or curative treatment. Curative applications may not be effective during periods of hot weather because the cool-season grasses are growing slowly and are unable to recover from damage under these conditions. Consider a preventive fungicide program when conditions favor disease development. For best results, initiate preventive applications in late spring or early summer when night temperatures consistently exceed 60°F (16°C).

Fungicides are often available in different formulations. Most of the time they are formulated to be applied through a sprayer; however, granular versions can be applied using a rotary spreader. When in doubt, hire a landscape professional. They are licensed and trained on how to best apply these products.

Pathogen — Clarireedia spp. (fungus)

Hosts — All turfgrasses

Overview

Dollar spot is a fungal disease of most cool-season and warm-season turfgrasses. On turf mowed higher than ½ inch, the spots in the landscape may expand 6 inches or more in diameter. The affected leaves typically remain upright and are characterized by white or light-tan lesions with light-reddish-brown margins. As the lesions expand, the leaves are girdled and the upper parts of the leaves die slowly. The grass in the spots may be killed to the soil surface if the disease continues to develop, and many spots may merge to produce large, blighted areas. Short, fuzzy, white mycelium is often observed on affected turf in the morning when dew is present.

The dollar spot fungus begins to grow and infect susceptible grasses in the spring when night temperatures exceed 50°F (10°C), even though symptoms of the disease may not appear until later in the spring or early summer. In addition, the pathogen requires extended periods of leaf wetness (10 to 12 continuous hours). Heavy dews that often form during cool nights in late spring or early summer create conditions most conducive to the disease. Extended periods of wet, overcast weather can also lead to severe dollar spot epidemics on susceptible grasses. Dollar spot remains active throughout the summer in many areas, but disease activity typically slows when temperatures consistently exceed 90°F (32°C). Turfgrasses that are deficient in nutrients, especially nitrogen, are more prone to dollar spot and also recover from the damage more slowly than well-fertilized turf. The disease is also encouraged by drought stress, low mowing, excessive thatch accumulation, frequent irrigation, and low air movement. Certain cultivars of creeping bentgrass, perennial ryegrass, and Kentucky bluegrass are very susceptible to dollar spot, while others are fairly tolerant.

Cultural Control

Use of resistant cultivars is one of the most effective means of managing dollar spot. In particular, creeping bentgrass, perennial ryegrass, and Kentucky bluegrass cultivars vary widely in their susceptibility to the disease. Base your turfgrass selection on university recommendations or regional cultivar trials conducted by the National Turfgrass Evaluation Program. When planting cool-season grasses, use blends and mixtures of multiple species and varieties whenever possible. Adequate nitrogen fertilization will help prevent dollar spot and encourage plants to recover quickly from the disease if it occurs. Select nitrogen sources, rates, and timings based on local university recommendations for your turfgrass species and climate. More nitrogen or less nitrogen may be required for your location depending on soil type, rainfall amounts, traffic intensity, and management practices. Deficiencies in other nutrients that limit foliar growth may also exacerbate dollar spot problems. Use soil test results to apply the recommended amounts of phosphorus, potassium, lime, and micronutrients. Dollar spot is triggered by drought stress and leaf wetness. Proper irrigation timing is needed to balance these factors. Irrigate based on the moisture status of the soil, not on a calendar schedule. If needed, irrigate early in the morning, between midnight and 6:00 a.m., to keep leaf wetness periods as short as possible. Mowing, dragging, or whipping the turf in the morning to remove dew can help prevent dollar spot, but these practices can spread the disease if it is actively developing. Improve air movement and reduce humidity by pruning trees, clearing unwanted vegetation, or relocating desirable plants. Excessive thatch accumulations greatly encourage dollar spot activity. Remove excess thatch by vertical mowing or power raking. Dollar spot is readily spread in leaf tissue or clippings from infected areas. To avoid spreading the disease, wash equipment before entering an uninfected area, and remove and dispose of clippings taken from infected areas.

Chemical Control

Many fungicides control dollar spot, but preventive applications are most effective. A preventive program should be implemented in early spring when night temperatures consistently exceed 50°F. When used as a curative, fungicides must be applied at high rates and short application intervals.

Uniform spray coverage is important for maximizing fungicide performance; even small gaps in coverage may allow dollar spot to develop. Nozzle type, nozzle pressure, and dilution rate have the greatest impact on the uniformity of fungicide applications. Nozzles that produce coarse to extremely coarse droplets dramatically reduce the performance of fungicides for dollar spot control. Air-induction or flat-fan nozzles that produce fine to medium droplets are recommended. To provide thorough coverage of the turfgrass foliage, fungicides should be applied in 2 gallons of water per 1,000 square feet; lower carrier volumes reduce the performance of fungicides for foliar disease control.

The fungus that causes dollar spot develops resistance to fungicides quickly. To prevent or delay the onset of fungicide resistance, use IPM to minimize fungicide use and rotate among fungicide classes after each application.

Fungicides are often available in different formulations. Most of the time they are formulated to be applied through a sprayer; however, granular versions can be applied using a rotary spreader. When in doubt, hire a landscape professional. They are licensed and trained on how to best apply these products.

Pathogen — Many different species of basidiomycete fungi

Hosts — All turfgrasses

Overview

The symptoms of fairy ring are patches, rings, or arcs in the turf that are initially 1 foot or less in diameter. However, they expand in size year after year, reaching up to several hundred feet in diameter in old turf stands. Most fairy ring fungi do not infect or parasitize the turf. Instead, growth of these fungi in the soil can indirectly affect, or even kill, the turfgrass above. Three types of fairy ring symptoms are observed in turfgrasses: Type I, Type II, and Type III. A Type I fairy ring causes the soil and thatch to become hydrophobic (water-repellant), killing the turf in patches, rings, or arcs. In areas affected by a Type I fairy ring, the thatch and soil are extremely dry and repel water. Type II fairy rings appear as rings or arcs in turf that are dark green and grow faster than the surrounding turf. In a Type III fairy ring, mushrooms or puffballs are produced in a ring or arc. The type of symptoms expressed by a particular fairy ring may change during the year according to weather conditions. Type III fairy ring symptoms are more prevalent during extended periods of wet weather. Type I and Type II fairy ring symptoms are most common during hot, dry weather in the summer.

Some of the fungi that cause fairy rings are wood-rotting fungi that grow on stumps, dead tree roots, waste lumber, or other woody materials. Once established, the turf produces thatch and organic matter, which provide a source of food for continued expansion of the fairy ring. Mushroom fungi are also prolific spore producers and may be spread into turf stands by wind or water.

Type I fairy rings are most damaging to turf. Most cases of Type I fairy ring are caused by hydrophobic residues that are produced as the fairy ring fungus grows through the soil. In other cases, ammonium nitrogen that is released into the soil by fairy ring fungi may accumulate in the soil at toxic levels. Either way, the expression of Type I symptoms can be further encouraged by drought stress, inadequate irrigation, and infrequent aerification.

Type II fairy ring symptoms are a result of the release of nitrogen and other nutrients into the soil when organic matter is degraded by the fairy ring fungi. These symptoms are most evident in turf that is deficient in nutrients, especially nitrogen and iron.

Type III fairy ring symptoms are most common after periods of heavy or frequent rainfall. They may occur more frequently in areas that are poorly drained or overirrigated.

Cultural Control

In landscape turfgrasses, the most effective means of fairy ring control is to prevent the causal fungi from becoming established in the turf. Remove large pieces of woody material (for example, stumps, waste lumber, and dead tree roots) before turf is planted to prevent the establishment of fairy rings. Landscape contractors should remove this debris around new construction sites before seeding or sodding the turf. Sterilization or fumigation of the root zone mix has not been effective in preventing or delaying fairy ring establishment.

Power raking or vertical mowing to remove excessive thatch will help minimize fairy ring problems. Avoid extremes in soil moisture (too wet or too dry), apply nitrogen amounts based on local university recommendations, and ensure balanced fertility through regular soil testing.

Once a fairy ring appears, the best management practices depend on the type of symptom that is observed. To control a Type I fairy ring, the water-repellent thatch and soil beneath the affected turf must be rewet. Hollow-tine aerification, spiking, application of soil surfactants, and heavy irrigation are effective strategies for rewetting this hydrophobic layer. Affected areas should be hand-watered to prevent overwatering of the surrounding unaffected turf.

Symptoms of a Type II fairy ring can be masked with an application of nitrogen or iron. This will cause the surrounding turf to green up, making the affected turf less evident. Collect soil or tissue samples for nutrient analysis from the turf immediately surrounding the Type II fairy rings, and correct any nutrient imbalances as recommended. Use caution when applying nitrogen to mask Type II fairy ring symptoms on cool-season grasses during in summer. Too much nitrogen may overstimulate the grass and lead to the development of more serious diseases. To avoid overstimulation of the grass, iron should be used to increase turf color without causing excessive foliar growth.

Drastic methods for control of fairy rings, such as soil fumigation, removal of infested soil, or turf renovation by tilling and mixing the soil, may be effective in the short term, but the fairy rings usually become reestablished over a period of years.

Chemical Control

More than 60 species of fungi have been associated with fairy ring symptoms in turfgrasses, and these species likely vary in their sensitivity to fungicides. Control of fairy rings with fungicides is a site-specific venture. Turfgrass managers should experiment with different products to identify those that will control the disease in their location.

Fungicides are most effective for fairy ring control when used on a preventive basis. Curative applications have little effect because the symptoms are caused by a change in the soil environment, and fungicides do nothing to change the soil. A preventive fungicide program should be initiated in the spring when mean daily soil temperatures are consistently above 55°F (13°C). Regular use of soil surfactants will help maintain uniform soil moisture and may reduce the appearance of Type I fairy ring symptoms.

Because fairy ring fungi are in the thatch and soil, fungicides must be watered-in or applied in large volumes of water for best results. Applications in 2 gallons of water per 1,000 square feet followed by 1/8 to 1/4 inch of irrigation have provided excellent results in research trials. Irrigation must be applied immediately before the spray begins to dry on the turfgrass foliage. Tank-mixing some fungicides with a soil penetrant may also enhance movement into the soil and improve fairy ring control.

Fungicides are often available in different formulations. Most of the time they are formulated to be applied through a sprayer; however, granular versions can be applied using a rotary spreader. When in doubt, hire a landscape professional. They are licensed and trained on how to best apply these products.

Pathogen — Pyricularia grisea (fungus)

Hosts — perennial ryegrass, St. Augustinegrass, and tall fescue

Overview

Gray leaf spot initially appears as spots on the leaves that are round or oval, are tan in color, and have a dark-brown border. When the leaves are wet or humidity is high, the leaf spots turn gray and fuzzy with profuse spore production. In time, the leaf spots expand and girdle the leaf, causing it to die back from the tip. Significant damage to the turf stand may occur as the disease continues to progress. In tall fescue and perennial ryegrass, foliar blighting initially occurs in patches from 4 to 12 inches in diameter that are orange to yellow in color. Like the leaf spots, these patches rapidly coalesce to produce large, irregular areas of damaged turf. The leaves of tall fescue and perennial ryegrass blighted by gray leaf spot are typically matted and greasy in appearance. Because of this symptom, gray leaf spot is often confused with Pythium blight in tall fescue and perennial ryegrass. Gray leaf spot does not develop in distinct patches in St. Augustinegrass, but affected leaves may wither and die, causing a brown cast to the turf that is visible from a distance.

Gray leaf spot is most severe in newly established turfgrass stands. The disease is typically most severe in the first year of establishment, then gradually becomes less damaging as the turf matures. Turfgrass hosts vary widely in their susceptibility to damage from gray leaf spot. Perennial ryegrass is most rapidly affected by infection, with widespread turf loss occurring in a period of a few days. St. Augustinegrass is most resistant, and rarely sustains significant damage if properly managed. Tall fescue has an intermediate level of resistance to gray leaf spot. In St. Augustinegrass, gray leaf spot is most active from June through August. In tall fescue and perennial ryegrass, most cases of the disease appear from late July through September. Gray leaf spot may develop when temperatures are between 70°F and 95°F (21°C to 35°C), but the fungus also requires at least 14 hours of continuous leaf wetness to initiate infection. Any factor that increases the amount of leaf wetness will increase development of gray leaf spot, including extended periods of cloud cover, improper irrigation timing or frequency, or extended rainfall. Lush leaf tissue produced by turf that is fertilized with excessive nitrogen is extremely prone to infection by the gray leaf spot pathogen.

Cultural Control

Cultivars of tall fescue and St. Augustinegrass vary considerably in gray leaf spot susceptibility. Perennial ryegrass cultivars with resistance to gray leaf spot are starting to become available. Refer to the results of cultivar evaluation trials operated by the National Turfgrass Evaluation Program or local universities for resistant cultivars that perform well in your area.

Managing leaf wetness is an effective means of minimizing gray leaf spot in all hosts. Schedule irrigation early in the morning, before sunrise, and never in the late afternoon or evening. Prune or remove trees, shrubs, or other barriers to increase air movement and sunlight penetration.

Proper mowing practices are most important for managing gray leaf spot in St. Augustinegrass. This grass must be mowed frequently during the summer months to remove excess leaf tissue, keep the canopy open and dry, and remove developing gray leaf spot lesions. Collecting clippings reduces spread of the disease when gray leaf spot symptoms are evident. Apply nitrogen and other nutrients as recommended to maintain vigorous foliar growth during the summer months. Excessive shade, in addition to promoting leaf wetness, slows St. Augustinegrass growth and enhances gray leaf spot problems.

Stress of any kind will encourage gray leaf spot development in tall fescue and perennial ryegrass. Proper mowing, fertilization, and irrigation practices will reduce the chances of significant turf loss from this disease. Mow to recommended heights, using the “1⁄3 rule” as a guide for mowing frequency. To reduce further spread of the disease, collect clippings when gray leaf spot is active. Do not apply nitrogen to susceptible grasses in late spring or summer. When establishing a new stand of tall fescue or perennial ryegrass, use recommended seeding rates to encourage rapid maturation of new seedlings.

Chemical Control

Since perennial ryegrass can sustain serious damage in a short period of time, preventive fungicide applications are recommended for gray leaf spot control. A preventive program should be initiated in mid-June or early July in most locations, with repeat applications at 14- to 21-day intervals. Monitor tall fescue frequently for gray leaf spot development so that fungicides can be applied to stop epidemic development. Resistance to the QoI fungicides (azoxystrobin, fluoxastrobin, pyraclostrobin, and trifloxystrobin) has been documented in gray leaf spot, therefore it is necessary to rotate through multiple chemical classes when managing this disease, including the use of tank-mixtures.

Fungicides are often available in different formulations. Most of the time they are formulated to be applied through a sprayer; however, granular versions can be applied using a rotary spreader. When in doubt, hire a landscape professional. They are licensed and trained on how to best apply these products.

Pathogen — Pythium spp. (water mold/oomycete)

Hosts — bluegrasses, fescues, ryegrasses

Overview

Pythium blight first appears as small, sunken, circular patches up to 1 foot in diameter during hot, humid weather. Leaves within affected areas are matted, orange or dark gray in color, and greasy in appearance. Gray, cottony mycelium may be seen in the infected areas when the leaves are wet or humidity is high. The disease spreads rapidly along drainage patterns and can be transferred by equipment. This disease can cause widespread damage to a turf stand very quickly if conditions are favorable for development.

Pythium blight may develop when night temperatures exceed 65°F (18°C) and leaves are continually wet for 12 to 14 hours for several consecutive nights. For this reason, severe Pythium blight epidemics are commonly observed the morning after a late afternoon or early evening thunderstorm in the summer. Daytime temperatures above 85°F (29°C) also encourage Pythium blight development, possibly due to increased stress. Excessive soil moisture and succulent foliar growth also favor disease development. Perennial ryegrass and annual bluegrass are most prone to Pythium blight and can sustain significant damage in two to three days when conditions are favorable. Creeping bentgrass and tall fescue are more resistant to the disease but can be severely affected if conditions are conducive for prolonged periods.

Cultural Control

Reduce prolonged leaf wetness by watering in the early morning hours, before sunrise. Avoid excessive rates of nitrogen to prevent lush, succulent foliar growth, which is very susceptible to Pythium blight. Cool-season turfgrasses should not be fertilized with more than 0.25 lb N per 1,000 square feet when conditions favor Pythium blight activity. Avoid establishing turf in low-lying areas that will collect water. If necessary, install subsurface drainage to prevent wet soil conditions. To minimize thatch accumulations, relieve compaction and maintain soil drainage through hollow-tine aerification. To minimize spread of the pathogen, do not mow or irrigate when Pythium mycelium is present on the foliage. Collect and promptly dispose of clippings from infected areas and ensure that mowing equipment is washed before going to an uninfected area.

Chemical Control

Due to the potential for rapid development of this disease, high-value areas and susceptible grasses should be protected with a preventive fungicide program. For cool-season turf, initiate applications when night temperatures consistently exceed 65°F (18°C) and repeat at 14- to 21-day intervals when conditions are favorable for Pythium blight development.

Fungicides are often available in different formulations. Most of the time they are formulated to be applied through a sprayer; however, granular versions can be applied using a rotary spreader. When in doubt, hire a landscape professional. They are licensed and trained on how to best apply these products.

Pathogen — Laetisaria fuciformis (fungus)

Hosts — Fine fescue, Kentucky bluegrass, tall fescue, perennial ryegrass

Overview

Red fungal strands ("red threads") develop in circular or irregular patches from 4 inches to 2 feet in diameter. Affected leaves within these patches are tan or bleached-white in color. From a distance, the patches usually have a reddish appearance due to the presence of thick, red strands of fungal growth emanating from the affected leaves. Through production of these threads, called sclerotia, the fungus spreads to healthy plants and survives unfavorable conditions. Small tufts of pink, fuzzy mycelium may also be present in or around the patches when the leaves are wet or humidity is high. After prolonged periods of disease development, the patches may merge to produce large, irregularly shaped areas of damaged turf.

The red thread fungus is able to cause disease at temperatures ranging from 40°F to 80°F (4°C to 27°C) but develops most rapidly at approximately 70°F (21°C). Red thread affects grass that is growing slowly for any reason, including inadequate fertilization, drought stress, cool weather, low light, excessive traffic, and pests. Red thread is most severe in the spring and fall, when extended periods of cool, wet, and overcast weather slow growth of the turf and favor growth of the pathogen. Because of its wide temperature tolerance, red thread can develop any time of year that a slow-growing host and sufficient leaf wetness are present.

Cultural Control

Fertilize to meet the nutritional needs of the turf and maintain vigorous growth. Submit a soil sample for nutrient analysis regularly, and apply recommended amounts of phosphorus, potassium, and lime. Apply nitrogen quantities based on university recommendations to prevent weak, thin turf; however, avoid overstimulation and the development of lush, succulent turf. Irrigate between midnight and 6:00 a.m. to prevent prolonged periods of leaf wetness. Never irrigate in the late afternoon or early evening. Apply enough water to wet the entire root zone, then reapply when the turf shows first signs of drought stress. Prune or remove trees, shrubs, or other barriers to increase air movement and sunlight penetration. To reduce spread of the disease, remove clippings from affected areas when the disease is active, and wash infected clippings off equipment before entering uninfected areas.

Chemical Control

Fungicides are available for control of red thread, but they are usually not necessary if proper cultural practices are implemented.

Pathogen — Puccinia spp. (fungus)

Hosts — Kentucky bluegrass, St. Augustinegrass, tall fescue, zoysiagrass

Overview

Early symptoms include small, yellow flecks that develop on the leaves and stems. The flecks expand over time into raised pustules that are yellow or orange in color; the pustules then rupture to release powdery masses of spores. Infected plants become yellow and are more susceptible to environmental stress. Heavily infected turf thins and releases clouds of orange dust (rust spores) when the foliage is disturbed. The rust pustules on infected leaves turn black during fall in preparation for overwintering.

Rust fungi survive the winter in living plant tissue from which new spores are produced in the spring. Spores produced in spring, summer, and fall are spread by the wind, germinate on the leaves, and infect new tissue. Extended periods of leaf wetness are required for the spores to germinate and for the disease to develop rapidly. Rust diseases are most severe in turf that is growing slowly due to adverse weather conditions or inadequate management. Low light, inadequate fertilization, drought stress, and infrequent mowing encourage rust development.

Cultural Control

Whenever possible, plant rust-resistant varieties to reduce this turf disease. Select cultivars based on regional trials and university recommendations. When planting cool-season turf, use blends and mixtures of multiple species or varieties whenever practical. Plant shade-tolerant grasses and increase mowing heights in heavily shaded areas.

Prune trees and remove unwanted undergrowth to improve air movement and reduce prolonged leaf wetness. Mow the turf regularly, removing no more than one-third of the foliage in one mowing. Collect and dispose of clippings taken from infected areas to slow the spread of rust.

Fertilize to meet the nutritional needs of the turf. Submit a soil sample for analysis regularly and apply recommended amounts of phosphorus, potassium, and lime. Apply nitrogen in accordance with university recommendations.

Water deeply but infrequently to encourage deep rooting and reduce drought stress and extended periods of leaf wetness. Avoid watering the turf before sunset or after sunrise.

Chemical Control

Fungicides can be used on a preventive or curative basis for rust control. Susceptible turfs should be monitored regularly for rust development during periods of cool and cloudy weather.

Fungicides are often available in different formulations. Most of the time they are formulated to be applied through a sprayer; however, granular versions can be applied using a rotary spreader. When in doubt, hire a landscape professional. They are licensed and trained on how to best apply these products.

Fungicide Management

• Pest Control for Professional Turfgrass Managers
• North Carolina Agricultural Chemicals Manual
• NC State Extension TurfFiles

Disease Diagnostic Resources

Diagnostic services for turfgrass diseases are available through NC State Extension. Visit the Turf Pathology Turf Diagnostics Lab website for instructions on submitting samples for testing.

Cultivar Trial Information

National Turfgrass Evaluation Program

Soil Testing Resources

NCDA&CS Agronomic Services Division, Soil Testing Section