Pest of the Month: Red Thread

By Richard Rees, Ph.D.

What does it look like?

Red thread, also known as “pink patch,” is a foliar disease that most often occurs on taller mown turfgrass. The disease appears in turf as small pinkish-red spots or patches, usually in the spring or fall, with symptoms often disappearing during the heat of the summer. Upon infection, areas turn light tan, and the leaf tips become covered with fine pink or red threads, thus causing the turf to have an overall pink complexion. These pinkish threads are caused by the fungus Laetisaria fuciformis/Corticium fuciforme.  Red threads can extend to about an inch past the height of the grass and typically spread through the turf in an area about 4 to 8 inches in diameter.

Host material and range

Red thread lawn disease is common in tall fescue grass and perennial ryegrass. Bermudagrass, bentgrass and Kentucky bluegrass are also sometimes affected. Outbreaks are prone to occur in turf that requires less maintenance, such as residential lawns and unkempt athletic fields. It usually occurs in the cooler and more humid areas of the Pacific Northwest, Northeast and Midwest. Red thread has the capability to take over a turf area very quickly, and leaves may begin to die two days after becoming infected. This quick influx results from the spread of the infected tissue and bits of the disease to healthy areas of grass by mowing and foot traffic on the diseased turf. During dry conditions, the threads may be visible for up to two years.

Current threat

 The disease is most severe on slow growing, nitrogen-deficient turfgrass during damp weather. The spreading of red thread is accelerated when turfgrass nutrition is poor and there is a lack of nitrogen or low levels of calcium. The lawn’s range of temperature also greatly affects disease development. Red thread occurs over a relatively wide range of temperature conditions, usually between 40 to 70 degrees, but most frequently in the 65 to 75 degree range. Although red thread creates an undesirable appearance on turf grass, the crowns and roots of the grass are not infected by the disease. Therefore, plants will not be killed and with proper treatment the turf can eventually recover.

Prevention tips

Due to the fact that nutritional imbalances in the soil can speed up the development and spread of red thread lawn disease, use a high-quality fertilizer with adequate nitrogen percentage. In addition, a well drained lawn helps avoid prolonged periods of leaf wetness, which will minimize the extent to which red thread patches expand. It is also vital to aerate your lawn using a hollow spike lawn aerator during the fall months.

Treatment tips

Once the lawn is infected, it is important to mow and burn the grass clippings collected from the infected area. In most cases, a fungicide treatment is unnecessary, but wet weather can sometimes cause severe damage. Therefore when disease is severe, fungicide applications may be necessary.

What can you do?

The most important strategy to effectively prevent, manage, and treat red thread is to maintain adequate soil fertility. The actual fertilization rates depend on the type of grass, soil texture and the specific rates recommended in your region. Another important practice to remember is to avoid both over-watering and watering your lawn in the late afternoon or evening. It is also critical for the health of your lawn to always provide good soil drainage. Additionally planted trees and shrubs should be far enough apart to prevent large areas of grass from being shaded for long periods during the day. This will also allow dew and other moisture on the grass to readily evaporate.

Richard Rees, Ph.D., is product development manager — fungicides at Bayer Environmental Science, a business group of Bayer CropScience LP. Armada fungicide from Bayer Environmental Science can be applied for control of red thread (apply .6-1.2 ounces at an interval of 14-28 days. Always read and follow label directions).

All photos courtesy of Bayer Environmental Science.

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