Turfgrass Diseases: Pink Patch (Causal Fungus: Limonomyces Roseipellis)

This disease is caused by the fungus Limonomyces roseipellis and is a common turfgrass disease during rainy periods in late spring and early summer. Pink patch often occurs with another disease called red thread, which has similar symptoms and develops under the same environmental conditions as pink patch. Control measures are similar for both diseases. Pink patch is usually found in perennial ryegrass, fine fescue, and Kentucky bluegrass lawns that do not receive adequate amounts of nitrogen fertilizer.

Symptoms and Signs

Pink patch symptoms appear as circular or irregular-shaped patches of blighted turf, typically with a pink cast. The disease is usually restricted to the leaves, leaf sheaths, and stems of turfgrasses. In advanced stages, leaves become covered with fluffy pink fungal mycelium. Diseased areas on leaves can take on yellow or bleached-straw color. In most cases, pink patch-affected turf is not severely damaged and recovers later in the growing season.

Disease Cycle

The causal fungus of pink patch disease, L. roseipellis, overwinters as dormant mycelium on dead leaves and stems of previously infected plants. The mycelium resumes growth when sufficient moisture and warmer temperatures return in spring. The fungus enters grass leaves through natural openings called stomata, by direct penetration of leaves, or through wounds. Mycelium on infected plants can be transported by mowers and foot traffic to other plants.

Disease Development

Pink patch disease tends to develop when air temperatures are 65° to 75°F and during prolonged periods of rainy or humid weather in late spring and early summer. Pink patch develops under the same environmental conditions as red thread disease and both diseases are often observed in lawns at the same time.

Cultural Control

Where pink patch disease occurs, fertilization with adequate nitrogen for good turf growth usually will reduce the injury. However, turf managers should be aware that excessive nitrogen additions can lead to other disease problems later in the season, including brown patch and Pythium blight. In most cases, turf affected by pink patch will recover within a few weeks. Lawns planted to cultivars of perennial ryegrass, Kentucky bluegrass, and/or fine fescues that are highly susceptible to pink patch can sustain significant damage and be slow to recover.

Chemical Control

In most situations, pink patch is not sufficiently damaging to warrant fungicide treatment. In rare cases, high-value lawns may become severely blighted during wet weather. In such cases, fungicide treatment will minimize symptoms.

*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. 2020. 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.