Department of Crop and Soil Sciences - Cooperative Extension
Turfgrass Diseases
Pink Snow Mold and Fusarium Patch, Microdochium nivale
Pink snow mold and Fusarium patch are diseases caused by the fungus Microdochium nivale. Pink snow mold is the name used to describe the disease associated with snow cover, appearing when snow melts. Fusarium patch is the name of the disease that occurs without snow cover. The causal organism of these diseases, Microdochium nivale, was formerly known as Fusarium nivale. To avoid confusion, Fusarium was retained as the disease name.
Symptoms of pink snow mold on annual bluegrass putting green.
Symptoms and signs
Pink snow mold is a true snow mold since it develops under snow cover. The disease gets its name from the accumulation of pink fungal spores that pile up on the leaves of infected grass plants, producing a pink cast on circular patches of matted grass. Usually only leaves are attacked, but under conditions favorable for disease development the fungus may kill the crowns and roots as well. Thus, pink snow mold can be more severe than gray snow mold.
Matted foliage of pink snow mold-affected turf.
Fusarium patch is similar in appearance to pink snow mold except that the centers of the patches are not usually as matted. Often, a fluffy growth of mycelium can be observed around the periphery of the patch. During periods of cool, wet weather from October to April, Fusarium patch may appear when temperatures are in the 40° to 50° F range. If pink snow mold develops in the cold, wet weather in early fall, the fungus may continue its activity through the winter and into spring. Damage to the turf is then likely to be quite severe and long-lasting.
Disease cycle
The fungus survives warm dry weather as dormant fungal mycelium or as dormant spores in soil and thatch. Spores germinate in cool, wet conditions, producing hyphae that infect grass leaves.
Cultural control
Pink snow mold usually can be managed successfully in home lawns without fungicides provided the lawn has been established for more than a year. Mow on a regular schedule well into the fall, and avoid high unclipped grass that tends to fall over and mat under snow cover. Try to avoid creating snow banks when removing and piling snow from sidewalks and driveways. Straw mulches and piles of leaves provide a favorable environment for pink snow mold and should be removed from the lawn before snow fall. In general, creeping bentgrass and perennial ryegrass are most susceptible to this disease, whereas Kentucky bluegrass and the fine fescues are only moderately susceptible.
Fusarium patch is typically only a problem on golf courses and can be managed by maintaining a balanced fertility program and avoiding excessive nitrogen applications in mid-fall.
Chemical control
Fungicide treatment may be needed to control pink snow mold and Fusarium patch in new turfgrass seedings or if a history of unmanageable outbreaks is known. On golf courses, fall or spring fungicide applications may be needed in cold, wet weather.
Powdery Mildew, Erysiphe graminis
Symptoms and signs
This fungus first appears as isolated wefts of fine, gray-white, powdery growth on the upper surface of the grass leaf. This growth rapidly becomes more dense and may cover the entire leaf, giving the leaf a gray-white appearance. In severe outbreaks, entire portions of the turf stand may be dull white, rather than green. Individual leaves look as though they are covered with flour or white powder.
Signs of powdery mildew fungus on Kentucky bluegrass.
Disease cycle
The organism overwinters in dead grass and in infected living grass plants. Spores of the fungus spread by wind to leaves of other turfgrass plants. Conditions favorable for the development of powdery mildew include poor air circulation, high atmospheric humidity (but no free water on the leaf surfaces), low light intensity or shade, and cool air temperatures. Kentucky bluegrass, when planted in shaded areas, is particularly susceptible to this disease.
Cultural control
Where occurrence of powdery mildew is frequent, changing landscape plantings to improve air drainage and reduce turf shading will aid in disease reduction. Prune overstory trees to allow sunlight to reach the turfgrass. Turfgrass species differ in their susceptibility to powdery mildew. Kentucky bluegrass, for example, is quite susceptible to this disease, whereas the fine fescues and tall fescue are quite resistant.
Chemical control
Fungicides, except for highly managed turf areas, are not necessary.