Pink snow mold
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.