Turfgrass Diseases: Pink Snow Mold (Causal fungus: Microdochium nivale)

This disease is caused by the fungus Microdochium nivale and results in patches of blighted turf on golf courses, athletic fields, and lawns. Pink snow mold can affect all cool-season turfgrass species and is common during years where a thick layer of snow cover lasts for long periods during mid to late winter. Microdochium nivale also causes a disease with similar symptoms to pink snow mold, except that disease activity does not occur under snow cover. This disease is referred to as Microdochium patch (sometimes called Fusarium patch).

Figure 1. Patches of pink snow mold on bentgrass putting green. Photo: Peter Landschoot, Penn State

Symptoms and signs

Pink snow mold symptoms and signs are first noticed as snow cover melts and exposes turf in late winter or early spring. Symptoms include pink, white, or tan patches of dead and matted leaf blades inside of an outer ring of copper-colored turfgrass plants. Patches typically range from 2 inches to 10 inches in diameter, sometimes coalescing to damage large areas of turf. White fluffy fungal mycelium can often be observed on the periphery of patches close to receding snow cover and during periods of high humidity in late winter or early spring. Pink snow mold can be distinguished from other snow mold diseases by the presence of pink coloration of leaf blades resulting from fungal mycelium and tiny spore-bearing structures called sporodochia, which can sometimes be observed with a powerful hand lens.

Figure 2. Pink snow mold patches on annual bluegrass golf course rough (left), and an individual patch of pink snow mold on an annual bluegrass putting green showing copper-colored leaves on the periphery of patch and pink and tan matted leaves in the inner portion of the patch (right). Photos: Peter Landschoot, Penn State

Figure 3. Matted leaves from the inner portion of a pink snow mold patch showing pink coloration of leaf blades. Photo: Peter Landschoot, Penn State

Disease cycle

Pink snow mold disease begins with the infection of turfgrass leaf tissues by mycelium of M. nivale residing on plant debris in the soil. Mycelium spreads from plant to plant under snow cover causing infections that result in patches of blighted leaves, stems, and crowns. Spores (conidia) formed in sporodochia on diseased tissues can give rise to new infections and form patches, even after snow cover is no longer present. Microdochium nivale survives as dormant mycelium in leaf litter, thatch, and soil during spring, summer, and fall. Pink snow mold is more likely to occur under snow cover when the soil is not frozen.

Disease development

Pink snow mold is commonly found in areas of greatest snow accumulation. Typically, the deeper the snow cover and the longer the snow remains on the turf surface, the greater the extent of symptom development and turfgrass injury. Ideal conditions for the development of pink snow mold include temperatures slightly above freezing at the snow/turf interface and wet leaf tissues. Once snow melts and no longer covers the turf, disease activity usually subsides but can become active again if cold, wet, and overcast conditions persist. This disease is usually most severe on close-cut turf, such as golf course putting greens, tees, and fairways; lush turfgrass maintained with high amounts of nitrogen fertilizer, and recently seeded grasses that have not completely matured prior to winter. In most cases, mature turfgrass affected by pink snow mold recovers when temperatures warm and leaf growth resumes in spring.

Cultural control

Cultural practices that may lessen the severity of pink snow mold include keeping turf mowed in late fall, avoiding the creation of long-lasting snowbanks on high-quality turf, and using only moderate amounts of nitrogen fertilizer in fall. When symptoms appear on high-cut turf in the spring, diseased areas can be raked to break-up the crusted, matted leaves. Nitrogen fertilizer can be applied to pink snow mold-affected areas to enhance turfgrass recovery. Although all cool-season turfgrass species are susceptible to pink snow mold, annual bluegrass, creeping bentgrass, and perennial ryegrass tend to be most severely injured.

Chemical control

Preventative fungicide applications can be used to control pink snow mold on high-value turf, such as golf course putting greens, tees, and fairways; sports fields; and recently seeded lawns. To obtain successful control, fungicides should be applied prior to the first permanent snow cover in the fall, typically in late November. Fungicide applications on pink snow mold-affected areas after snow melts are usually not needed unless conditions become conducive to continued disease activity.

Some penetrant fungicides labeled for control of pink snow mold disease.

Some multisite contact fungicides labeled for control of pink snow mold disease.

Some combination product fungicides labeled for control of pink snow mold disease.

*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 the 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 a 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, use 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.

Smith, J. D., N. Jackson, and A.R. Woolhouse. 1989. Fungal diseases of amenity turfgrasses. 3rd ed. E. and F. Spon, London.