PESTS of Ornamentals and Turfgrass
Kentucky Pesticide Safety Education Program
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Dr. Ric Bessin
Dept. of Entomology
University of Kentucky


Visits since 11/11/16

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Diseases of Turfgrass

Accurate identification and diagnosis of plant diseases is an art, as well as a science, and experience is essential. This section will acquaint you with the general symptoms of diseases of turfgrass. For more accurate disease diagnosis, consult your county Extension agent.

Numerous disease problems occur on turfgrass in Kentucky and these frequently cause extensive damage. In many cases, a disease is blamed for poor quality turf when, in reality, it may be only a contributing factor or not involved at all. Frequently, dead and dying grass is caused by improper fertilization, chemical burn, mower problems, dog or insect injury, dry or wet spots, thatch, competition from other plants, or from any other improper management. Accurate diagnosis of the problem is essential for proper control.

Two types of pathogens (fungi and nematodes) are found in turf in Kentucky. Observation of symptoms is an important aid in determining which pathogen is causing a disease. The following information will explain the identification and biology of some common turf diseases.

Helminthosporium Leaf Spot

Helminthosporium leaf spot
“Football” shaped leaf lesions of leaf spot and melting out of Kentucky bluegrass
photo: S. Tirpak, Rutgers

Helminthosporium leaf spot is a common disease problem of Kentucky bluegrass and is often referred to as “melting-out.” Other Helminthosporium leaf spots are important on fescues and bermudagrass. From a distance, leaf spot-affected areas appear chlorotic or yellowed. Individual spots on the leaves have dark margins with tan centers. The spotting is most noticeable in spring and early summer.

Infection in the crown of the plant during the summer can lead to the death of plants (thus “melting-out”). Cool, wet weather during spring followed by drought during summer accentuates the damage from this disease.

Dollar Spot

Dollar spot
Dollar spot appears as sunken round, bleached-out or straw-colored spots.
photo: Michigan State Plant Pathology

Dollar spot affects a wide variety of grasses, including Kentucky bluegrass, bermuda, perennial ryegrass, zoysia, tall fescue, and bentgrasses. The fungus is active throughout the growing season, especially when there is low soil moisture and an excess of dew or fog. It is most prevalent in the spring.

The disease is characterized by small white patches, one to three inches in diameter A large number of spots can come together and form larger dead areas. Leaf spots are usually found along the edges of the grass blade and may come together across the blade, causing the tip to die. Individual leaf spots are tan with reddish margins.

Pythium Blight

Pythium blight
Pythium blight
photo: William M. Brown, Jr.,

Pythium blight is caused by a number of species of the fungus Pythium. The fungus primarily attacks perennial ryegrass and bentgrass although other grasses can be affected. Conditions that favor Pythium blight include abundant moisture and poor air circulation. The disease is most active in hot, humid weather when the night temperature does not go below 70°F.

The blight appears first as small spots a few inches in diameter. Diseased leaves are at first water-soaked, soft, and slimy, and may mat together. Dense, cottony fungal growths often are apparent in affected areas during a heavy dew. The leaves soon shrivel and the color of the patch soon fades to light brown as dew dries. The shape of the diseased area may be streaked following the drainage flow of water over the turf.

Brown Patch

Brown patch
Brown patch on bentgrass
photo: U Mass

Brown patch is a common fungal disease of fescues, perennial ryegrass and bentgrass. It develops most readily when daytime highs exceed 80°F and nighttime lows are in the mid- 60’s°F or higher.

Brown patch is one of the more common turf diseases, especially in tall fescue. In addition to ideal temperatures and humid weather, heavy applications of nitrogen fertilizer favor disease development.

Brown patch is characterized by nearly circular areas of dead leaves that may be a few inches to several feet in diameter. On closely mown turf, the edges of the dead area may have a gray, smoky color, particularly in early morning. Affected areas are generally tan or brownish in bent and ryegrass. Affected fescues usually have straw-colored leaves.

Summer Patch

Summer patch
Summer Patch
photo: Mary Ann Hansen, Virginia Polytechnic Institute and State University,

Summer patch affects Kentucky bluegrass and annual bluegrass. Circular to irregular patches of dead turf up to 1-2 feet in diameter develop during hot weather in mid- to late-summer. Below ground, roots and crowns of affected plants are brown and decayed, a result of fungal colonization. A tuft of healthy, green grass is sometimes evident in the center of affected patches, giving them a characteristic “donut” appearance.

Necrotic Ring Spot

Necrotic ring spot
Necrotic Ring Spot
photo: Howard F. Schwartz, Colorado State University, Bugwood.orgg

Necrotic ring spot is another disease of bluegrasses with symptoms similar to summer patch. In contrast to summer patch, symptoms of necrotic ring spot can develop following cool, wet weather in late spring or mid-autumn. Necrotic ring spot is less common in Kentucky than summer patch.


Rust on turfgrass
Rust pustules on turfgrass
photo: Iowa State

Rust is sometimes a problem on Kentucky bluegrass, fescue, zoysia, perennial ryegrass, and bermuda grasses. Rust infection results from rust spores which are blown to the plant from distant areas or from nearby alternate hosts. Large numbers of spores are produced in the leaf spot (pustule). These spores are then the source of new infections.

The disease is most frequently found during cool, humid weather during autumn. Grass varieties differ in susceptibility to rust.

Red Thread

Red thread
Red thread
photo: Bruce Watt, University of Maine,

Red thread is seen as irregularly shaped patches of blighted turfgrass, ranging from a few inches to a few feet in diameter. Often, as diseased leaves turn brown, pink or reddish fungal growth can be observed on the leaf surface or emerging from the cut ends of leaves. This disease affects most of the common grasses grown in Kentucky and is often found during spring and early summer. The disease is favored by conditions of low nitrogen fertility.

Mushroom Fairy Ring

Mushroom fairy ring
Mushroom fairy ring
photo: Clemson University - USDA Cooperative Extension Slide Series,

Mushroom fairy ring can occur in any turf. The ring appears as a circular discoloration of grass from several inches to many yards in diameter. Mushrooms (toadstools) may appear at the edge of the ring during warm, moist periods).

The ring of grass is generally a darker green than the grass inside and outside the ring. During periods of moisture stress, the grass inside the ring may die. This general decline of grass inside the ring adds to the unsightliness of the fairy ring problem. Fairy rings gradually increase in size.

Slime Molds

Dog vomit slime mold
Dog vomit slime mold
photo: Sandra Jensen, Cornell University,

Slime molds are commonly found on lawns in warm, moist weather. This fungal growth on grass leaves may be either a small, crust-like, light to dark mass with a sooty appearance, or a tan to orange shapeless mass.

The fungus causing this unsightly problem does not infect the grass blade; it simply uses it for support. The only effect it has on the plant is to temporarily reduce food production by the grass leaf as a result of shading.


root-gall nematodes
Root-gall nematodes on Kentucky bluegrass
photo: Bonsak Hammeraas, NIBIO - The Norwegian Institute of Bioeconomy Research,

Nematodes weaken and reduce the vigor of turfgrass by restricting the development of the root system. The symptoms of nematode injury may be confused with nutritional problems, insufficient water, hardpan, or any factor that restricts root development.

Symptoms commonly associated with nematode injury include thinned or completely killed areas, pale green to chlorotic color, excessive wilting during drought stress, poor response to fertilization, and a greater weed problem due to sparse grass.

The intensity of the symptoms will vary with the grass variety, the kinds of nematodes present, the nematode population level, and the fertilization-watering program being practiced. The most reliable method for determining whether a nematode problem exists is by a soil assay. Nematode damage to turfgrass is uncommon in Kentucky.




Practice Questions


1) Which of the following causes a plant disorder?

  1. fungus
  2. bacteria
  3. nematode
  4. nutrient deficiency
2) _________ are the most common infectious organisms causing plant disease.
  1. Bacteria
  2. Fungi
  3. Sunscalds
  4. Viruses

3) _________ reproduce by spores.

  1. Nematodes
  2. Bacteria
  3. Fungi

4) _________ reproduce by simple cell division.

  1. Bacteria
  2. Fungi
  3. Nematodes

5) _________ is an example of a fungal disease.

  1. Root cyst
  2. Mosaic pattern on leaves
  3. Root rot
  4. Leaf blight

6) ________ diseases are commonly spread by aphids or leafhoppers.

  1. Virus
  2. Mildew
  3. Abiotic
  4. Root rot

7) Wilting is an example of a disease sign.

  1. True
  2. False

8) Infection begins when the pathogen ___________.

  1. enters the plant
  2. arrives at a part of the plant where infection can occur
  3. symptoms appear

9) _________ move from plant to plant on in water droplets, rain splash, or being carried by insects.

  1. Fungi
  2. Viruses
  3. Bacteria
  4. Nematodes

10) Powdery mildew, root rots, and stem rots are examples of diseases caused by __________.

  1. fungi
  2. bacteria
  3. nematodes
  4. viruses

11) Most problems with dead and dying turfgrass grass are due to diseases.

  1. True
  2. False

12) From a distance, areas of turfgrass affected by ____________ appear chlorotic or yellowed; individual spots on the leaves have dark margins with tan centers.

  1. dollar spot
  2. white grubs
  3. Helminthosporium leaf spot or melting out
  4. brown patch

13) __________ is characterized by small white patches, 1 to 3 inches in diameter that may join to form larger dead areas of turfgrass.

  1. brown patch
  2. dollar spot
  3. white grubs
  4. Helminthosporium leaf spot or melting out

14) ___________ appears during hot weather in mid- to late-summer as circular to irregular patches of dead turf 1 to 2 feet in diameter.

  1. Summer patch
  2. Rust
  3. Slime mold

15) _________ diseases usually produce pustules on plant leaves.

  1. Mosaic
  2. Bacterial
  3. Rust
  4. Virus

16) Leaf rust is rarely is an explosive problem because it develops so slowly.

  1. True
  2. False

17) _________ is the first step in disease management.

  1. Waiting for symptoms to appear
  2. A correct diagnosis
  3. Selection of the most effective fungicide

18) Many different plant diseases cause similar symptoms.

  1. True
  2. False

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