Microdochium Patch

Disease

Pink snow mold

Microdochium nivale

Photos

This is the most important disease in areas with extended periods of cool wet weather. Symptoms appear as reddish brown to copper-colored spots in the turf. Without snow cover, the spots range in diameter from less than 1 in. (2.5 cm) to about 8 in. (20 cm) in diameter. With snow cover, the circular spots are usually 2-3 in. to 1-2 ft. (5-7.6 cm to 0.3-0.6 m) in diameter, and are tan to reddish brown. Pink mycelia of the fungus can often be seen shortly after snow melt near the margin of the infected patch.

The pathogen can survive as mycelium and spores in the thatch and will actively grow on the grass residue until infection takes place when temperatures are below 60° F (15.5° C). Snow cover is NOT necessary for infection; cool wet periods (32-46° F [0-8° C]) especially those with alternating thawing, cold, fogs, and light drizzling rain are most conducive for disease spread.

Crops Affected: turf

Damage

The location of this disease is home lawns and golf courses. General symptoms are a circle, patches, spotting or irregular coloring. Foliar symptoms are browning and turning orange. This can occur during the months of January, February, March, April, May, June, September, October, November, and December. Hosts of the disease are Kentucky Bluegrass, Perennial Ryegrass, Tall Fescue, Fine Fescue, Creeping Bentgrass, Annual Bluegrass, and Colonial Bent.

Management

As with Typhula blight, lush turfgrass growth just before the snow mold season will make turf more susceptible to disease. Therefore, fertilizer applications should be timed accordingly to avoid such growth late into the season. Nitrogen applications should be scheduled early enough to give the turfgrass a chance to harden off before the snow or frost sets in, or before grass becomes dormant. Fall mowing to prevent turf matting can aide in eliminating a potential "microenvironment" conducive for disease development.
Many contact fungicides such as chlorothalonil and mancozeb can be used to manage pink snow mold where there is no lasting snow cover. Where snow cover persists for three or more months, systemic fungicides must be used. The DMI and dicarboximide fungicides are among some of the systemic fungicides shown to be effective in managing the disease; however, strains of M. nivale resistant to these fungicide chemistries have been reported.

MSU Extension Turf