Turfgrass Diseases: Microdochium patch (Causal Fungus: Microdochium nivale)

Microdochium nivale also causes pink snow mold, which has similar symptoms except that it occurs under snow cover, whereas Microdochium patch develops in the absence of snow cover.

Figure 1. Microdochium patch symptoms on annual bluegrass/bentgrass putting green. Photo: Peter Landschoot, Penn State

Symptoms and Signs

In Pennsylvania, Microdochium patch symptoms occur on occasion during early to late spring. Symptoms on putting greens and tees include pink or red patches of blighted leaf blades in circular or roughly circular patches, often with some healthy-appearing grass in the center. Patches typically range from 1 to 8 inches in diameter, sometimes coalescing to damage larger areas of turf. White fungal mycelium can sometimes be observed on the periphery of patches during periods of wet weather and overcast conditions.

Figure 2. Microdochium patch symptoms on annual bluegrass putting green (left), and an individual patch showing copper-colored leaves in the diseased area, and some healthy-appearing turf in the inner portion of the patch (right). Photos: Peter Landschoot, Penn State

Disease Cycle

Microdochium patch begins with infection of turfgrass leaf tissues by mycelium of M. nivale, which reside on plant debris in soil, or by germinating spores (conidia). Mycelium and conidia spread from plant to plant during wet, cool, and overcast conditions, causing infections that result in patches of blighted leaves, stems, and crowns. Conidia are formed in spore-bearing structures called sporodochia on diseased tissues and can give rise to new infections and form patches if favorable conditions persist. Microdochium nivale survives as dormant mycelium in leaf litter, thatch, and soil during spring, summer, and fall.

Disease Development

Microdochium patch typically occurs in early to mid-spring during extended periods of cool and rainy periods that result in long periods of moisture on leaf surfaces. Microdochium patch is found on close-cut turf, such as golf course putting greens and tees, but is not as common as some other spring foliar diseases, such as anthracnose and leaf spot. Annual bluegrass is the most common host of M. nivale and can be severely injured if conditions are ideal for disease development.

Cultural Control

Cultural practices that may lessen the severity of Microdochium patch include using only moderate amounts of nitrogen fertilizer in spring, removing moisture from leaf surfaces, and avoiding prolonged tarping of putting greens in spring.

Chemical Control

Fungicide applications can be used to control Microdochium patch on golf course putting greens and tees. To obtain successful control, fungicides should be applied as soon as symptoms become apparent.

*FRAC is an abbreviation for Fungicide Resistance Action Committee. The FRAC code/resistance group system consists of numbers indicating classes or groups of fungicides based on mode of action, and letters that refer to broad classifications of fungicides (P = host plant defense inducers; M = multi-site fungicides; and U = unknown mode of action and unknown resistance risk). Due to the risk of fungicide resistance, turf managers should avoid excessive use of fungicides within the same FRAC code/resistance group and alternate products among different FRAC codes/resistance groups.

**Plant mobility classification refers to a fungicide’s ability to penetrate plant surfaces or remain on plant leaf or stem surfaces without penetration. Fungicides that penetrate plant surfaces and are translocated mostly upwards through plant xylem tissues are called acropetal penetrants (acropetal = toward the apex). Fungicides that enter plant cuticles or move limited distances in internal plant spaces, but do not translocate through vascular tissues (xylem and/or phloem) are called local penetrants. Contact fungicides do not penetrate plant surfaces and only inhibit fungal pathogens residing on leaf and stem surfaces.

***Follow label precautionary statements, restrictions, and directions regarding tolerant turfgrass species, rates, and timing of applications.

References

Buhler, W. Fungicide spraying by the numbers.

Clarke, B.B., P. Koch, and G. Munshaw. Chemical control of turfgrass diseases 2020. University of Kentucky, Rutgers University, and University of Wisconsin.

Latin, R. 2011. A practical guide to turfgrass fungicides. American Phytopathological Society Press, St. Paul, MN.

Smiley, R.W., P.H. Dernoeden, and B.B. Clarke. 2005. Compendium of turfgrass diseases, 3rd Edition. American Phytopathological Society Press, St. Paul, MN.