Plant Disease Profile: Red thread

Looking closely at the circular, pink patches forming in turf, the human eye can see red filaments that are pretty obvious.

Those strands are a growing turf disease and responsible for the infection's name: red thread.

This unsightly, though not turf damaging, disease is caused by a fungus (Laetisaria fuciformis) that is common in all soil. It appears when turf isn't getting enough nitrogen but is taking in too much moisture.

To find out how to prevent and control grass from turning rosy, Lawn & Landscape spoke to Richard Latin, professor of plant pathology at Purdue University.
 

Growth and identification. Red thread grows out of the thatch in the soil under mild moist conditions and will infect leaves.

"Infection by this fungus is favored by periods of mild temperature and ample moisture during the growing season, so it can appear in spring, summer or fall," Latin says. "And in terms of ample moisture, it can be in the form of precipitation or heavy dews."

As the fungus grows, it produces a pink, cottony mycelium. As the infected turf leaves collapse and become desiccated, the fungus will produce little red filaments, Latin says.

The leaves collapse, forming patches in the yard. Red thread won't take over an entire yard but, at times, it can look severe.

"There are other diseases that produce cobwebby, cottony stuff – it could be white or it could be gray – but in the case of red thread, it definitely has a pink tint to it," he says.

Red thread can occur on all lawn grasses, but primarily is found on cool-season grasses like tall fescue, Kentucky bluegrass and perennial rye grass.
 

Prevention. Latin says he has yet to hear of any varieties of grasses less resistant to red thread. But, of course, there are ways to stay defensive against the disease.

"Red thread is often associated with a deficiency in nitrogen," Latin says. "Therefore, the lawn care professionals who are managing properties that have had an issue with red thread, I'm sure that they are making a very effective nitrogen application plan in the fall. But they should also consider supplemental nitrogen at the end of spring or early summer. This is especially for properties that have had a serious problem with red thread."
 

Control. In extreme cases, fungicides can be applied to kill the red thread and nurse the turf back to health.

"The first thing is to select an appropriate fungicide," Latin says. "The second thing, which is just as important, is to apply it at the right time. The right time is at the very first time that pink mycelium (appears) in the lawn."

Step number two might mean closely monitoring customers' lawns, especially ones with a history of red thread outbreaks.

"It takes several days, a week or so, before it gets extensive, so you really have to be there to monitor it closely and put that application down," Latin says.

There are two classes of fungicide that Latin says are effective on red thread: strobilurin and DMI.

"If a lawn care operator comes into a property that already has an extensive red thread outbreak, some of that fungicide will work well," Latin says. "But I always recommend some supplemental nitrogen there to help the turf recover from the infection that is there."

The author is an associate editor at Lawn & Landscape. She can be reached at clawell@gie.net.