There are many reasons to you could have dead patches in your lawn. The early spring snow melt sometimes reveals issues with turf that needs to be attended to.
Snow Mold is usually the culprit. Many people in our area call it “winter kill” however, the reality is a fungus that blooms under the snow pack and when the conditions are just right it will consume large areas of turfgrass if not properly controlled.
There are two varietes of Snow Mold. Pink and Grey Snow Mold. Here are some interesting facts from the University of Mass Turf Division:
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. incarnatahas 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 Typhulaspp., M. nivaledoes 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.
Some lawn care companies in our area recommend 5 treatments of fertilizer. However in some circumstances this may be warranted we do not recommend it as it can only further exacerbate the fungus. Ensuring that you mow your grass short after we receive several hard frosts in the late fall. In the spring time you should plan to rake your lawn immediately after the snow pack melts and before the green grass blades start popping up you will help prevent the dead spots on your lawn.
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