You Are Here: Management Updates 2009 Archive March 31, 2009

Date: March 31, 2009
Category: Diseases
Subject: Snow Molds

Snow molds are patch diseases caused by various cold-loving fungal pathogens and appear most often in early spring as snow melts.  Typhula blight and Microdochium patch are the two most common culprits on turf areas such as home lawns, sports fields and golf courses.  This year snow molds caused significant damage on turfgrasses throughout the New England region due to prolonged snow cover.  The following are some cultural practices for the management of snow molds.

• Typhula Blight (Gray and Speckled Snow Molds):

Pathogens:  Typhula incarnata, Typhula ishikariensis
Hosts:  Most susceptible - bentgrasses, annual bluegrass, tall fescue.  Moderately susceptible - perennial ryegrass, fine fescues. Least susceptible - Kentucky bluegrass, colonial bentgrass.
Optimum Conditions:  Cold (30-40º F), wet weather; prolonged snow cover; high nitrogen fertility.
Symptoms:  Melting snow reveals circular gray or straw colored patches from a few inches to three feet or more in diameter.  The grass in these areas is usually matted down and grayish-white mycelium is often visible at the edge of the patches.  Sclerotia (resting structures) of the fungi can often be found in and among the diseased grass blades.  Susceptible turfgrasses are usually severely thinned or may even be killed.  T. incarnata has large, rust-colored sclerotia, while the sclerotia of T. ishikariensis are smaller, spherical and black (about the size of a pinhead).
Cultural Control:  Plant less susceptible Kentucky bluegrass varieties (see UMass Snow Mold Field Day 2009 report) for home lawns, sports fields and/ or colonial bentgrass for golf courses fairways and tees.  Avoid heavy, (> 0.5 lb/1000ft2) late season applications of water-soluble nitrogen and continue to mow the grass until dormancy in the fall.  Manage excessive thatch and reduce soil compaction in the fall.  Avoid compacting snow where damage has previously occurred.  In the spring, rake and fertilize damaged areas to stimulate turfgrass regrowth from viable crowns since only leaves are killed in most cases.  Remove snow and improve drainage so that water melt from snow will dry rapidly in disease susceptible areas in early spring. Severely damaged turf may require reseeding.  Preventative fall fungicide applications are critical on highly managed turf areas.  Curative applications in late winter or early spring are usually not effective.

• Microdochium Patch (Pink Snow Mold)

Pathogen:  Microdochium nivale
Hosts:  Most susceptible - annual bluegrass, bentgrasses. Moderately susceptible - perennial ryegrass. Least susceptible - Kentucky bluegrass, fine fescues.
Optimum Conditions:  Cool-cold (30-60º F), wet weather; high nitrogen fertility; alkaline soils; snow cover (not necessary).
Symptoms:  Wet grass is covered with circular patches of tan to white grass from a few inches to a few feet in diameter.  The leaves of affected turfgrasses often mat together and pink mycelium is commonly visible at the edge of the patches.  Unlike Typhula spp., M. nivale does not produce sclerotia.  Mycelium and asexual spores (called conidia) of the fungus give the border of the patches a distinct pink to reddish brown color.  In the absence of snow cover, and when weather is cool and wet, water-soaked patches of grass one to a few inches in diameter are common.  These patches are grayish to white in the center with reddish-brown borders.  At higher temperatures (50-65º F), the fungus is capable of causing a yellow blighting of higher cut grasses during wet periods.
Cultural Control:  Plant less susceptible turfgrass species such as Kentucky bluegrass or fine-leaved fescues.  Avoid late season applications of readily available nitrogen and mow the grass until dormancy in the fall.  The disease is more severe under alkaline conditions, so maintaining a pH of 7.0 or less in the soil profile will reduce disease damage.  In the spring, rake and fertilize damaged areas to stimulate turfgrass regrowth.  Severely damaged turf may require reseeding.       

Submitted by: Dr. Geunhwa Jung

DISCLAIMER - As always, it is the responsibility of the applicator to verify the registration status of any pesticide BEFORE applying it. Different states have different regulations as well. The author and the University of Massachusetts are not liable for any consequences of any pesticide "recommendations". Mention of any trade name is not to be considered endorsement of a product.

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