Fusarium patch (Michrodochium nivale) is a serious disease of cool season golf and sports turf grasses (bentgrass, perennial ryegrass, annual bluegrass etc.)Fusarium patch is found mostly in regions with cool humid weather conditions due to the way the disease spreads and survives. The pathogen usually infests the thatch layer where the spores can be easily spread and survive. The mycelium is pink to rose in color; it normally attacks the shoots of the plant. It will survive in both live and dead plant tissue; the optimum pathogenicity temperature range is 32-44 degrees F (0-6 degrees C)
Research shows that the pathogen does not infect the crown or root of the plant, but only causes leaf blade damage. Therefore, if conditions are favorable for growth the grass will recover. In North America, Fusarium patch is often referred to as "pink snow mold". The pathogen, Microdochium nivale, is the causal agent of both Fusarium patch and pink snow mold. The term pink snow mold however is used when the disease occurs under snow or tarp or leaf cover, while the term Fusarium patch is used when snow cover etc. is absent.
Fusarium patch usually first appears as 1-2 inch (25-50mm) diameter water soaked circular patches. They can enlarge up to as much 12 inches (300mm) in diameter. The patches will start of with a yellow to orange-brown color. As the diseased patch gets bigger the center of the patch turns brown or tan in color. The patches can combine to form large circular or irregular shapes. When conditions are moist and the mycelium is active, there will sometimes be a ring of pink to white mycelium around the outside of the patch.