Pink patch is a fungal disease that affects turfgrass and was previously considered a form of red thread disease. It commonly coexists with red thread, as the two fungi share similar appearances and often develop together. The pathogen infects both warm-season and cool-season grasses from various genera, including Agrostis, Cynodon, Festuca, Lolium, Paspalum, and Poa.

Causal agents

Limonomyces roseipellis fungus

Primary Hosts

Agrostis, Cynodon, Festuca, Lolium, Paspalum, and Poa

Disease Cycle

The disease cycle of pink patch is similar to that of red thread. However, pink patch does not produce arthroconidia or sclerotia. The pathogen, Limonomyces roseipellis, can survive for extended periods as mycelium in infested plant debris.

The disease typically occurs during cool, moist weather in spring and autumn when temperatures range from 18-24°C (64-75°F). However, pink patch can occur at any time of the year as long as adequate surface moisture is present. The pathogen has a slow growth rate and is more damaging to unmowed or slow-growing turf.

Epidemiology

Pink patch is more severe in turfgrass maintained with low nitrogen fertility. It is commonly observed in the same stands of turfgrass where red thread is present. Both diseases can coexist. Pink patch is most prevalent during cool, moist weather conditions in the presence of surface moisture

Symptoms

Symptoms of pink patch include circular patches ranging from pinkish red to tan, with diameters of 5-10 cm. Unlike red thread, pink patch spreads slowly and causes less severe damage to the grass. It primarily affects a limited number of leaves, resulting in superficial damage that does not significantly reduce the growth rate of the grass. The affected leaves develop a pink, gelatinous growth of fungal mycelium, starting from the leaf margins and gradually expanding to cover the entire width of the blade. Infection can occur through stomata, direct penetration, or wounds. Infected leaves develop chlorotic lesions that expand and become water-soaked, leading to the death of the leaf from the tip towards the base. Affected sheaths and dead leaves may mat together, turning straw brown or tan. Unlike red thread, pink patch does not produce threadlike sclerotia or pink, cottony flocks of arthroconidia.

Credit: John Kaminski/Penn State University

Signs

The signs of pink patch include the presence of a pink, gelatinous growth of fungal mycelium on individual leaves. This growth initially develops along the leaf margins and gradually expands to cover the entire width of the blade. The mycelium appears as a pink-colored coating on the affected leaves and individual hypha have clamp connections.

Credit: John Kaminski/Penn State University

Management

In the management of pink patch, both cultural and chemical control practices play crucial roles. Cultural practices involve implementing various turf management techniques to create unfavorable conditions for disease development and promote turf health. These practices include proper irrigation, pruning, and mowing techniques. On the other hand, chemical control measures involve the strategic use of fungicides and proper nutrient management to suppress the disease and support turf recovery. By combining these cultural and chemical approaches, turf managers can effectively manage pink patch and maintain healthy and vibrant turfgrass.

Cultural

Irrigation should be applied as needed to prevent drought stress, with thorough and infrequent watering early in the day, avoiding prolonged leaf wetness. Pruning trees or shrubs and improving light penetration and airflow over the turf can be beneficial. Using sharp mower blades minimizes leaf tip wounds that may lead to infection. Removing turfgrass clippings during periods of active pink patch can help reduce the disease’s spread by eliminating some of the inoculum.

Proper management practices are essential for controlling pink patch. Maintaining adequate and balanced fertility based on soil or tissue tests is crucial. Applications of water-soluble, quick-release nitrogen can reduce the severity of pink patch and promote turf recovery. Soil pH should be within the recommended range for the specific turfgrass species (generally pH 6.0-6.5).

Chemical

The same fungicides effective against red thread can be used for pink patch.