Snow mold

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Snow mold is a type of fungus and a turf disease that damages or kills grass after snow melts, typically in late winter. [1] Its damage is usually concentrated in circles three to twelve inches in diameter, although yards may have many of these circles, sometimes to the point at which it becomes hard to differentiate between different circles. Snow mold comes in two varieties: pink or gray. While it can affect all types of grasses, Kentucky bluegrass and fescue lawns are least affected by snow mold. [2]

Contents

Environment

Snow mold is found in areas that experience extended periods of snow cover, such as northern North America, Europe, and Asia. [3] These areas cover the cool temperate and boreal regions of the Northern Hemisphere. Turfgrasses that are usually protected and kept moist by snow cover are endangered because of it. [4] In overcast, rainy conditions between 32 and 60 degrees Fahrenheit, the pathogen thrives, and grows under snow covering wet turf in unfrozen soil. The pathogen “overwinters” during the summer months, in the form of sclerotia. Then, when exposed to cool temperatures and a wet environment, such as in early spring during snow melt, it forms fruiting bodies (sporocarps) or mycelium and begins to spread. [5] The cold environment limits other biological activity, allowing Typhula spp. to thrive. [4]

Hosts and symptoms

Typhula spp. impacts cool season turfgrass that experiences extended periods of snow cover. [6] These species of hosts can include creeping bentgrass, annual ryegrass, and perennial ryegrass. Some of its more common hosts include fine fescue, tall fescue, and Kentucky bluegrass. [7] Symptoms of the pathogen often manifest in all species the same way; as circular patches 6 inches to a foot in diameter of dead or damaged turfgrass. [6] Sometimes patches can be as large as three feet and can merge into other patches. These “scars” in the turf can remain until May or early June. Dead plant tissue becomes matted and blades become grayish and brittle after drying. [5] [8] Signs of the disease can include visible mycelium on turf after snow clears and dark brown or black sclerotia structures embedded in dead plant tissue. [6]

Disease cycle

The disease often begins its cycle in the cool, wet months of October or November. During this time, the pathogen’s primary inoculum, mycelium from sclerotia, is produced. The sclerotia (identifiable by their distinct rind patterns) begin germination under correct temperature and UV light conditions. Carpogenic sclerotia produce spore-bearing structures known as clavula, which in turn produce basidia. The resulting basidiospores produce the mycelium. The pathogen also uses the sclerotia to “overwinter” during the summer and warmer months. [4] There is evidence that the fungus is systemic within the grass plant itself. In the spring, spores can also be spread by rain, wind, and human interaction. [8]

Management

Physically, snow mold can be managed by keeping grass cut to proper height recommendations. For bluegrasses, red fescues, and ryegrasses, this is 1 ½ - 2 inches and for bentgrasses, ½ inch or less. Mowing is recommended through autumn, until grass growth stops. Avoid thick thatch accumulation by power raking the turf frequently and avoid both synthetic and organic mulches. It may also be recommended to improve light exposure and air circulation by removing dense foliage such as trees or shrubs in the area. After snowfall, it is recommended to avoid large snow accumulation over turf, using snow fences or other barriers.

Chemically, management can include maintaining balanced fertilization. High potassium and phosphorus soil values are also recommended. Avoid nitrogen fertilization close to the first heavy snow. Common turf fungicides (including contact fungicides and systemic fungicides) should be used before the first heavy snow. [8] Fungicides may include benzimidazole, strobilurin, and phosphonate fungicides. However, it has been found that some pink snow molds are resistant to benzimidazole fungicides. [9]

Gray snow mold

Gray snow mold ( Typhula spp. or Typhula blight) is the less damaging form of snow mold. While its damage may appear widespread, it typically does little damage to the grass itself, only to the blades. [1] Unlike most plant pathogens, it is able to survive throughout hot summer months as sclerotia under the ground or in plant debris. [10] Typhula blight is commonly found in United States in the Great Lakes region and anywhere with cold winter temperatures and persistent snow fall. [11] [12]

Pink snow mold

Pink snow mold (Microdochium nivale or Fusarium patch) is the more severe form of snow mold, and can destroy the roots and crowns of grass, causing more damage than gray snow mold. [1] Like gray snow mold, it is able to survive the summer months in decayed plant debris as spores or mycelium. [10]

See also

Related Research Articles

<span class="mw-page-title-main">Fusarium patch</span> Plant fungal disease

Fusarium patch is a disease in turf grass settings also called pink snow mold or Microdochium patch. In many cool season grass species in North America, it is caused by the fungus Microdochium nivale. The white-pink mycelium on infected leaf blades is a distinguishing characteristic of the Microdochium nivale pathogen. Fusarium patch is considered economically important in the turf grass industry because of its tendency to cause significant injury to golf greens, thereby decreasing putting surface quality. Dissimilar from other snow molds, such as gray snow mold, Microdochium nivale does not need snow cover to cause widespread infection.

<i>Botrytis cinerea</i> Species of fungus

Botrytis cinerea is a necrotrophic fungus that affects many plant species, although its most notable hosts may be wine grapes. In viticulture, it is commonly known as "botrytis bunch rot"; in horticulture, it is usually called "grey mould" or "gray mold".

Pythium volutum is a plant pathogen infecting wheat, barley, and turfgrass. It is known to be sensitive to some of the compounds typically present in selective media commonly used for isolating Pythium spp., so isolation may require alternative methods.

Sclerophthora macrospora is a protist plant pathogen of the class Oomycota. It causes downy mildew on a vast number of cereal crops including oats, rice, maize, and wheat as well as varieties of turf grass. The common names of the diseases associated with Sclerophthora macrospora include “crazy top disease” on maize and yellow tuft disease on turf grass. The disease is present all over the world, but it is especially persistent in Europe.

<i>Sclerotinia sclerotiorum</i> Species of fungus

Sclerotinia sclerotiorum is a plant pathogenic fungus and can cause a disease called white mold if conditions are conducive. S. sclerotiorum can also be known as cottony rot, watery soft rot, stem rot, drop, crown rot and blossom blight. A key characteristic of this pathogen is its ability to produce black resting structures known as sclerotia and white fuzzy growths of mycelium on the plant it infects. These sclerotia give rise to a fruiting body in the spring that produces spores in a sac which is why fungi in this class are called sac fungi (Ascomycota). This pathogen can occur on many continents and has a wide host range of plants. When S. sclerotiorum is onset in the field by favorable environmental conditions, losses can be great and control measures should be considered.

<i>Typhula incarnata</i> Species of fungus

Typhula incarnata is a fungal plant pathogen in the family Typhulaceae.

Colletotrichum cereale is a plant disease (fungus) that has been found to cause crown rot anthracnose of turf grass most commonly occurring on golf courses. Anthracnose can occur as both a foliar blight and basal rot. This disease attacks the crowns of plants, which is different than other anthracnose diseases. Anthracnose of turfgrass can be a foliar disease or in this case a basal rot of the lower portion of the plant. It attacks different species of turfgrass throughout the world most commonly annual bluegrass and creeping bentgrass.

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<span class="mw-page-title-main">Brown patch</span> Fungal disease affecting turfgrasses

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Red thread disease is a fungal infection found on lawns and other turfed areas. It is caused by the corticioid fungus Laetisaria fuciformis and has two separate stages. The stage that gives the infection its name is characterised by very thin, red, needle-like strands extending from the grass blade. These are stromata, which can remain viable in soil for two years. After germinating, the stromata infect grass leaf blades through their stomata. The other stage is visible as small, pink, cotton wool-like mycelium, found where the blades meet. It is common when both warmth and humidity are high.

<i>Typhula</i> Genus of fungi

Typhula is a genus of clavarioid fungi in the order Agaricales. Species of Typhula are saprotrophic, mostly decomposing leaves, twigs, and herbaceous material. Basidiocarps are club-shaped or narrowly cylindrical and are simple, often arising from sclerotia. A few species are facultative plant pathogens, causing a number of commercially important crop and turfgrass diseases.

Dollar spot is a fungal disease of turfgrass caused by the four species in the genus Clarireedia, in the family Rutstroemiaceae. The pathogen blights leaf tissues but does not affect turf grass roots or crowns. There is evidence that a fungal mycotoxin produced by the pathogen may cause root damage, including necrosis of the apical meristem in creeping bentgrass. However, the importance of this toxin is unknown and its effects are not considered a direct symptom of dollar spot. The disease is a common concern on golf courses on intensely managed putting greens, fairways and bowling greens. It is also common on less rigorously maintained lawns and recreational fields. Disease symptoms commonly result in poor turf quality and appearance. The disease occurs from late spring through late fall, but is most active under conditions of high humidity and warm daytime temperatures 59–86 °F (15–30 °C) and cool nights in the spring, early summer and fall. The disease infects by producing a mycelium, which can be spread mechanically from one area to another.

Typhula blight is most commonly known as a turf disease, but can also be a problem with wheat. Typhula blight is caused by a Typhula fungus, either Typhula incarnata or T. ishikariensis. Typhula incarnata is the causal agent for gray snow mold and T. ishikariensis causes speckled snow mold. Snow molds are caused by cold tolerant fungi that require snow cover or prolonged periods of cold, wet conditions. Typhula blight is most notably found in the turf industry, affecting a wide range of turfgrasses. Upon the snow melt, gray circular patches of mycelium are found. These mycelia produce a survival structure called a sclerotia that survives the warm summer months. Typhula blight is commonly controlled with fungicide applications in the late fall and by other cultural practices. If unchecked, snow molds can cause severe turf loss.

<span class="mw-page-title-main">Turf melting out</span> Turfgrass disease caused by the pathogen Dreshlera poae

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<span class="mw-page-title-main">Common spot of strawberry</span> Plant fungal disease

Common spot of strawberry is one of the most common and widespread diseases afflicting the strawberry. Common spot of strawberry is caused by the fungus Mycosphaerella fragariae. Symptoms of this disease first appear as circular, dark purple spots on the leaf surface. Mycosphaerella fragariae is very host-specific and only infects strawberry.

<span class="mw-page-title-main">Brown ring patch</span> Fungal disease of turf grass

Brown ring patch is a recently described Rhizoctonia-like disease of turf grass caused by the fungus Waitea circinata var. circinata. The disease primarily affects putting greens and causes yellow or brown rings up to 1 metre (3.3 ft) in diameter. Brown ring patch was first observed in Japan and has since spread to the United States and China (2011).

Bacterial wilt of turfgrass is the only known bacterial disease of turf. The causal agent is the Gram negative bacterium Xanthomonas campestris pv. graminis. The first case of bacterial wilt of turf was reported in a cultivar of creeping bentgrass known as Toronto or C-15, which is found throughout the midwestern United States. Until the causal agent was identified in 1984, the disease was referred to simply as C-15 decline. This disease is almost exclusively found on putting greens at golf courses where extensive mowing creates wounds in the grass which the pathogen uses in order to enter the host and cause disease.

Necrotic ring spot is a common disease of turf caused by soil borne fungi that mainly infects roots (4). It is an important disease as it destroys the appearance of turfgrasses on park, playing fields and golf courses. Necrotic Ring Spot is caused by a fungal pathogen that is an ascomycete that produces ascospores in an ascocarp (6). They survive over winter, or any unfavorable condition as sclerotia. Most infection occurs in spring and fall when the temperature is about 13 to 28°C (5). The primary hosts of this disease are cool-season grasses such as Kentucky bluegrass and annual bluegrass (6). Once turf is infected with O. korrae, it kills turf roots and crowns. Symptoms of the disease are quite noticeable since they appear as large yellow ring-shaped patches of dead turf. Management of the disease is often uneasy and requires application of multiple controls. The disease can be controlled by many different kind of controls including chemicals and cultural.

Gray leaf spot (GLS) is a foliar fungal disease that affects grasses. In grasses other than maize it is caused by Pyricularia grisea, which only infects perennial ryegrass, tall fescue, and St. Augustine grass in places with warm and rainy climates.

References

  1. 1 2 3 "Snow Mold Fact Sheet". University of Rhode Island Landscape Horticulture Program. Archived from the original on 2012-09-06. Retrieved 2012-10-07.
  2. ↑ "RPD No. 404 - Snow Molds of Turfgrasses". Univ. of Illinois Extension. July 1997. Retrieved November 11, 2011.
  3. ↑ "snow mold | Description, Symptoms, & Control". Encyclopedia Britannica. Retrieved 2020-12-10.
  4. 1 2 3 Hsiang, Tom; Matsumoto, Naoyuki; Millett, Steve M. (September 1999). "Biology and Management of Typhula Snow Molds of Turfgrass". Plant Disease. 83 (9): 788–798. doi: 10.1094/PDIS.1999.83.9.788 . ISSN   0191-2917. PMID   30841033.
  5. 1 2 admin (2015-05-14). "The Snow Molds". Center for Agriculture, Food and the Environment. Retrieved 2020-12-10.
  6. 1 2 3 ""Turfgrass Disease Profiles" : Purdue" (PDF).
  7. ↑ [(https://www.thelawninstitute.org/pages/education/types-of-grasses-and-species-selection/cool-and-warm-season-grasses/#:~:text=Cool%20season%20grass%20species%20include,27%20to%2035%C2%B0C) "Choosing Between Cool and Warm Seasons Grasses: The Lawn Institute"].{{cite web}}: Check |url= value (help)
  8. 1 2 3 "IPM : Reports on Plant Diseases : Snow Molds of Turfgrasses". ipm.illinois.edu. Retrieved 2020-12-10.
  9. ↑ Vincelli, Paul (2014). "Chemical Control of Turfgrass Diseases 2014". University of Kentucky (UKnowledge).
  10. 1 2 Ash, Cynthia (February 2000). "SNOW MOLDS in LAWNS". University of Minnesota. Retrieved 2012-10-07.
  11. ↑ Kerns, J.P. (2011). "Turf diseases of the Great Lakes region" (PDF). Univ. of Wisconsin Extension. Retrieved November 11, 2011.
  12. ↑ Johnston, William H. (December 2003). "Snow Mold Control in the Intermountain Northwest" (PDF). U.S. Golf Association. Retrieved November 10, 2011.
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