Dr. Pete's Turf Tips
(aka Pink Snow Mold and Fusarium Patch) Sighted in February by Peter H. Dernoeden, Ph. D.
Microdochium patch is a disfiguring cold weather disease of turf. This disease has been referred to by at least three different names, because it can occur in the presence (i.e., pink snow mold) or absence (i.e., Fusarium patch) of snow, and because of changes in the Latin name of the pathogen. The disease was first known as Fusarium patch in the U.K., and as pink snow mold in the U.S. Pathologists argued that pink snow mold was an inappropriate name because the disease can occur in the absence of snow. The Latin name of this fungal pathogen is Microdochium nivale (formerly Fusarium nivale, and others). To clarify the confusion, Microdochium patch is now the accepted name for this disease, regardless of whether or not it is associated with snow cover.
Microdochium patch is most damaging to annual bluegrass, creeping bentgrass and tall fescue. In many cases, turf recovers from buds on stems. Microdochium patch is most destructive to cool-season grass seedlings and can be especially severe when seedlings are covered with blankets. It therefore is important to check under blankets frequently for the presence of this and other diseases.
Conditions favoring Microdochium patch include low (32-45°F) to moderate (46-65°F) temperatures; snow cover; prolonged periods of chilly, overcast and rainy weather; and shady, wet or poorly drained sites. The disease may appear anytime between autumn and spring, but in the mid-Atlantic it usually develops in late winter. Given the unusual weather pattern (especially snow followed by mild rainy periods) it appeared in February 2016.
The snow-free stage initially appears in spots 1 to 3” in diameter, which have a reddish-brown or bronze color. Patches can increase to 6” or more in diameter and blighted centers usually have a tan or bleached appearance. The peripheries of larger patches generally have a pink or reddish-brown color. When active, leaves are matted and some foliar mycelium may be evident on blighted tissues. Sometimes there are smoke rings.
When Microdochium patch develops under snow, and as snow recedes, turf at the fringe of the tan or white -colored patches appears pink. Patches developing under snow range from 3 to 18” in diameter. The pink appearance is produced by the salmon-pink color of the pathogen’s mycelium. The pink fringe around patches fades in time and may not be evident following the advent of sunny and drier conditions. Plants eventually collapse and leaves are matted. Matted leaves have a tan or white color, but on close inspection they may display a pale, pinkish cast. When the disease occurs under snow, the extent of injury usually is more severe than without snow cover.
Breaking mats with brushes and rakes, followed by an application of a modest amount of water soluble N when weather is warm enough to promote growth, will greatly speed recovery. Regardless of being a preventive or curative fungicide application, decades of research have shown a large benefit from tank-mixing an appropriate contact and penetrant fungicide.