Turf MD: Dr. D shares how superintendents can contend with snow mold
Late fall is a time of reflection for golf course superintendents in the cool temperate regions of the United States. Post-summer stress management practices have been completed, and routine management practices have slowed, reflected in the slowing of turf growth. This lull is only a precursor to the most important disease control sprays of the season — those targeted at snow molds.
Karl Danneberger, Ph.D
Snow molds in the northern U.S. are the most serious turfgrass diseases a superintendent will face. Due to the cold weather, snow molds often cause damage out of sight of golfers and stealthily under the cover of snow. The optimum time to control snow molds in the northern U.S. is after turf growth stops and before the first heavy snowfall.
The two main snow molds are Typhula blight and Microdochium patch. In the cool temperate regions of the country and the world, Microdochium patch causes the greatest damage to courses.
Cool, wet conditions found through early fall into early spring — 32 to 46 degrees F — are ideal for the pathogen Microdochium nivale to infect turfgrasses, leading to Microdochium patch. What makes this disease more prominent is that, unlike other major snow molds, a snow cover is not required.
Locations where wet cool conditions are extensive like areas in the United Kingdom, or New Zealand, Microdochium patch severity extends beyond a “traditional” winter season.
Although turf managers commonly know this disease as pink snow mold, when it occurs under a snow cover, the official name is Microdochium patch (also formerly referred to as Fusarium patch). Microdochium patch is especially active on golf courses where annual bluegrass predominates, especially in shaded, wet, north-facing areas. In general, young, juvenile or lush turf is more susceptible than mature stands.
Microdochium patch initially appear as small patches, maybe 1 to 2 inches in diameter, that eventually reach 12 inches in diameter. Leaves become water-soaked and turn reddish-brown, then bleach-colored. In cool, wet weather, the leaves are matted together, especially on high-cut turf that becomes covered with a whitish-pink mycelial growth that is slimy when wet. The pink mycelium is often observed in the early morning. The circular patches may exhibit a pink coloration when exposed to light.
The pathogen, Microdochium nivale, is a profuse spore producer. Incredible spore loads develop around infected turf areas. These huge spore buildups may manifest in late winter or early spring along drainage ways, which, with moving water, can produce “streaks” of infected turf. Sometimes, these streaking patterns are misdiagnosed as cool-temperature Pythium. Cultural practices can help reduce the severity of Microdochium patch. Given that matted turf is more prone to it, regular mowing until the turf ceases growth would be recommended. Mulching or removing leaves from the turf can help reduce a wet, moist environment for the disease to develop under the leaf cover. Leaf removal in rough, shaded areas can help reduce the conditions favorable for disease.
On golf courses that use winter covers on greens, monitoring conditions under the covers is important. Microdochium patch can appear on greens that are subjected to humid and warmer conditions under the cover. In cases where disease might be expected, a preventative fungicide application would be suggested prior to covering.
Where Microdochium patch is a chronic and severe problem, preventive fungicides would be recommended. The first fungicide application is the most critical, as it helps reduce the spore population (inoculum level), slowing disease development over time.
This is an effective strategy in the United Kingdom, where Microdochium patch is a severe problem. A late summer or early fall application can slow Microdochium patch development, and subsequent applications help moderate the disease.
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