RED THREAD AND PINK PATCH DISEASES OF TURFGRASSES

Agronomy Mimeo 86Revised February, 1989

 

INTRODUCTION

Red thread and pink patch are common diseases of turfgrasses in Maryland, and are generally among the first diseases to appear in early spring. Development of these diseases is favored by cool (65-70 F), wet weather in the spring and fall. These diseases may also occur during warm or very cool to cold weather in the presence of plenty of surface moisture or at snow melt in February and March. They also occasionally occur during prolonged overcast and drizzling rainy weather in the summer. These diseases become widespread among turfgrass species during mild winters. Red thread is caused by the fungus Laetisaria fuciformis; whereas, pink patch is caused by one of two species of the fungus Limonomyces.

Red thread and pink patch have become more common and widespread in recent years and are now considered diseases of significant economic importance in the U.S. The recent and severe outbreaks of these diseases can be attributed to the more widespread use of perennial ryegrass. In the past, perennial ryegrass was not commonly used as a turf; however, the advent of the improved "turf-type" cultivars has led to their acceptance as a turfgrass species. Unfortunately, perennial ryegrass is perhaps the most susceptible turfgrass species to these diseases. Red thread and pink patch are also quite damaging to the fine leaf fescues, which are principally used in Maryland as minor components in Kentucky bluegrass mixtures. Bentgrasses may be badly damaged by these diseases during early spring at snow melt or in the presence of plenty of moisture under cool environmental conditions. Red thread and pink patch also attack Kentucky bluegrass, tall fescue and bermuadgrass, but seldom cause a significant level of injury to these species.

 

SYMPTOMS

The symptoms and signs of red thread are distinctive and unmistakable. In the presence of morning dew or water from rain, a corral pink or reddish layer of gelatinous fungal growth (mycelium) can easily be seen on leaves and sheaths. Upon closer inspection, the green leaves of invaded plants develop a water-soaked appearance. When leaves dry, the fungal mycelium becomes pale pink in color and is easily seen on the straw brown or tan tissues of dead leaves and sheaths. During the final phases of disease activity, bright red, hard and brittle strands of fungal mycelium called 'red threads' or sclerotia may be seen extending from leaf surfaces, particularly leaf tips. These red threads fall into the thatch and serve as resting structures for the fungus, which survives long periods that are unfavorable for growth of the pathogen. Once favorable conditions for disease activity recur, these sclerotia germinate by producing mycelium and the disease cycle is again initiated. The fungal mycelium primarily enters plants through open stomates. From a distance, affected turf has a straw-brown, tan or pinkish-tan color that appears in circular or irregularly shaped patches 2 inches to 3 feet in diameter.

Pink patch symptoms are usually less conspicuous than those of red thread. The pink patch fungi do not produce 'red threads' and mycelium generally appears as a faint pink color on diseased leaves. Affected patches of turf can range one to six inches or more in diameter and usually develop a straw brown or pale pink color. The pink patch fungi penetrate leaf tissues directly rather than entering plants through stomates. Pink patch fungi are often found in association with red thread.

 

CULTURAL CONTROL

Red thread and pink patch are generally more injurious on poorly nourished turfs. Frequently, these diseases are best controlled by an application of 0.5 to 1.0 lb N/1000 ft2 using a readily available, water soluble nitrogen source. Application of nitrogen during periods too cool for turf growth will not aid in reducing disease severity. This is because nitrogen reduces the injurious effects of the disease by stimulating plant growth and vigor. Evidently, the fertilized plants are able to replace damaged tissues more rapidly than the fungus can inflict injury. Excessive usage of nitrogen fertilizer in spring, however, may enhance red thread and other turf diseases, and reduce the environmental stress tolerance of plants during summer.

Little is known regarding the relative levels of susceptibility of perennial ryegrass cultivars to red thread, and no information on cultivar sensitivity to pink patch is available. Results of a perennial ryegrass performance trial, conducted by VPI and SU in 1987, indicated that Omega II, Palmer, Derby, Prelude, Birdie II, Pennant and Ranger possess good red thread resistance.

Employment of a balanced fertility program and environmentally adapted, disease resistant cultivars are the best approaches to the control of turf diseases. Despite hard work and use of proper cultural practices, red thread and pink patch may become injurious and fungicides are then needed to control the disease. There are several fungicides available that will effectively control red thread. It is likely that pink patch can be controlled with the same fungicides recommended below for red thread.

CONTACT FUNGICIDES
PENETRANT FUNGICIDES
Chipco 26019
Bayleton
Daconil 2787
Banner
Dyrene
Heritage

ProStar

In most home lawn situations, a single application of a contact fungicide should provide sufficient disease control. Under more intense cultural systems such as golf courses, fungicides may require reapplication on 10 to 14 day intervals on an as needed basis.

Mimeo prepared by Peter H. Dernoeden, Extension Turfgrass Specialist, Department of Agronomy