As the snow has begun to melt away over the past two or three weeks, many of you may have noticed the appearance of circular or irregular, blighted turf caused by various psychrophilic (cold-loving) turfgrass pathogens that cause snow molds. Typhula blight (caused by Typhula spp.) and Microdochium patch (caused by Microdochium nivale) are the two most common turfgrass diseases found on home lawns, sports fields and golf courses after snowmelt. This year snow molds have caused significant damage to turfgrass throughout the New England region due to prolonged snow cover (over three months in some areas). Below are some guidelines for indentifying snow mold type and recommended management practices.
Typhula blight also known as gray snow mold is mainly caused by two different snow mold species (Typhula incarnata and Typhula ishikariensis). Typhula blight is more prevalent under longer periods of snow cover and is likely to be the dominant snow mold in the northern regions that experience greater than three months of snow cover. Three main features are used to distinguish Typhula blight:
- Melting snow reveals circular gray or straw colored patches from a few inches to three feet or more in diameter. Turfgrass that is taller than 2 inches may exhibit symptoms that look irregular (Fig A and B).
- Grass is usually matted down and grayish-white mycelium is often visible at the edge of the patches.
- Sclerotia (resting structures, red/pink in color) of the fungi can often be found in and among the diseased grass blades (Fig C).
Since Typhula blight favors snow cover and cooler temperatures (just above freezing), further infection is unlikely by now. The most appropriate measure is to lightly rake damaged areas to increase air circulation and promote light penetration, which will increase new growth and recovery. This practice should not be done if the areas are still wet. Light to moderate nitrogen application will also help the recovery. Severely damaged areas may require reseeding. Fungicide application is not recommended since neither Typhula species will be causing further infection.
Microdochium patch caused by Microdochium nivale infects turfgrass under a wider range of temperatures (32-48° F) and is capable of causing further damage during cool, wet periods during the spring. Microdochium patch can be distinguished as follows:
- Wet grass is covered with circular patches of tan to white grass from a few inches to a few feet in diameter (Fig D).
- Grass matted together and pink mycelium is commonly visible at the edge of the patches.
- In the absence of snow cover, and when weather is cool and wet, water-soaked patches of grass with one to a few inches in diameter are common. These patches are grayish to white in the center with dark-brown borders.
In most situations (landscape, home lawn, golf course rough and fairways), fungicide application is not warranted and light raking/light nitrogen application is the best course of action. However, high maintenance turf situations (putting greens and tee boxes) may warrant fungicide application to prevent further damage. Due high soil moisture levels, applications should be made with lightweight fungicide delivery systems to minimize soil compaction. Fungicide application is only necessary if cool, wet conditions persist and Microdochium patch is already present. If you have questions about fungicide selections for snow mold control, please contact the UMass Turfgrass Pathology Lab (firstname.lastname@example.org or 413-577-3303).
A) Typhula blight - Patches are slightly irregular due to taller turfgrass.
B) Typhula blight - Patches are more circular due to shorter turfgrass.
C) T. incarnata red/pink sclerotia. A key diagnostic feature in the field.
D) Microdochium patch with characteristic pink and brown borders.
Submitted by: Dr. Geunhwa Jung