Melting snows revealed some significant snow mold damage. As you know there are two types of snow mold diseases, gray snow mold (aka Typhula blight) and pink snow mold (Microdochium patch). Although they create similar symptoms (circular patches of tan turf—sometimes with orange/brown margins) the pathogens are not closely related and they have different temperature requirements for infection. Infection by the gray snow mold pathogen occurs within a narrow range of cold temperatures (32 – 36 degrees Fahrenheit). The insulating effect of snow cover offers extended periods when such temperatures are maintained at the turf surface. Gray snow mold is not common in Indiana, but I have found plenty of it where snow piles have remained all winter. The gray snow mold pathogen produces survival structures called sclerotia that are about the size of a period printed on this page.
Pink snow mold is much more common in the lower Midwest because infection occurs under a wide range of temperatures (32F – 50F). Symptoms that develop after snow melts, during cold wet weather in spring are attributed to the Microdochium patch phase of the disease. The pathogen produces spores (called conidia) at the edge of circular patches. The conidia may be washed down slope to create new infections, especially on putting greens. Juvenile (less than one year old) creeping bentgrass is unusually susceptible to snow mold damage.
At this time of year, controlling gray snow mold is all about hastening recovery of the patches. Because of the narrow range of temperatures required for infection, the disease will not spread any more this year. Disturbing (raking) the matted turf and perhaps a light application of N will accelerate turf growth as temperatures rise and mitigate the effects of the disease.
We treat pink snow mold differently because it remains a threat through April and May. I do not think fungicides are warranted for fairways, but I would consider an application on tees and putting greens if numerous patches developed over the winter. Turf within the patches are thinned by disease progress and therefore are vulnerable to colonization by Poa annua. It is likely that only a contact fungicide (chlorothalonil) will limit spread while turf remains dormant. Once turf is actively growing, a penetrant fungicide (such as a DMI) may provide more effective control.
For more details about snow mold diseases check out our Turfgrass Disease Profiles on the Turf Program Website— https://turf.purdue.edu/