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Red Thread Fungus & Lawn Disease (How to Treat Laetisaria Fuciformis)

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Written By: Mark Marino, a Massachusetts Core Applicator License holder
and owner/operator of Lawn Phix,

No AI pledge. Authored and reviewed by Mark, not robots. Learn more.

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LAWN PHIX PRO TIPS

With this year’s excessive rain and overcast, I witnessed a lot of red thread in the spring of 2023. Here are a few quick bullet points on managing red thread disease in your lawn.

  • Red Thread thrives in the springtime with prolonged wetness on grass blades, limited sunlight, and lack of nitrogen.
  • Fine fescue, in particular, is the most susceptible cool-season grass to red thread fungus.
  • Prolonged red thread will form mycelium, which looks like pink cotton balls on the turf.
  • A quick-release nitrogen fertilizer can help “push out” the unsightly red thread.
  • Preventative and curative applications of fungicides containing propiconazole, azoxystrobin, or myclobutanil should be applied to help treat and stop the growth of red thread.

How to get rid of Red Thread Lawn Disease

Generally occurring during humid periods of spring and fall, red thread fungus disease can leave your lawn looking blighted with irregular shapes of pink patch. Once grass blades affected by the fungus die, they fade to a dull, bleached-out tan hue. Red thread fungus disease most frequently affects Bermuda grass, bentgrass, perennial ryegrass, Kentucky bluegrass, and fescues. Red thread like structures underscore the active infection of red thread disease. Fortunately, there are some disease management strategies that can help get rid of this fungal disease. Read on to learn more. 

What Is Red Thread Fungus?

Lawns are at greatest risk of red thread fungus in the spring, but it can also occur in the fall and even winter. Laetisaria fuciformis grows with sufficient warmth and moisture. The disease is generally spread from leaves or stems from the previous growing season that are affected with red thread disease. The disease usually enters grass blades at their cut tips. Once it does, it quickly spreads to the rest of the plant. Often, it’s foot traffic and mowers that spread the mycelium. 

The heavy or persistent periods of spring rains contribute to the growth of red thread disease. Red thread fungus is sometimes confused with red patch as both diseases feature similar symptoms. 

Signs of Red Thread Fungus

Red thread fungus is marked by signs such as pinkish red grass blades, the grass blades appear to have a ragged look, and irregularly shaped patches will break out. The patches tend to grow up to about three feet in diameter, filled up with infected grass. As the fungal disease progresses, its ‘red threads’ tend to become more pronounced. After it rains or your lawn is irrigated, the grass will appear a darker red. As it dries, it takes on its pink hue. Infected blades show ‘antler-like’ threads. The mycelium might appear weblike, especially when lawn conditions are wet and the weather is humid.

It’s important to note that the fungal disease moves through each infected grass blade quickly. Red thread fungus can kill infected grass blades in as few as two days, with temperature and humidity playing key roles in the disease development and spread.

Red Thread Disease Cycle

Lawns are vulnerable to red thread fungus when conditions are between 65-75 degrees Fahrenheit. While many fungal turf diseases spread by spores, red thread spreads by mycelium which have laid dormant in the lawn or are spread by foot traffic or mowers. Once the disease cycle begins, the grass begins to develop the red sclerotia quickly, and the grass can blades can die within a couple days if left untreated.

How to Control Red Thread Fungus

The best way to control red thread is by supporting lush, healthy grass using best lawn care practices. Inadequate fertilization can leave the lawn susceptible to red thread. Heavy foot traffic and insufficient sunlight also contribute to this lawn disease. Trimming trees to allow for more sunlight penetration through the canopy may help reduce the risk of fungal lawn diseases. Use the following methods to control red thread fungal growth.

Cultural Red Thread Fungus Control

  • Raise your mower and sharpen the blades to reduce stress
  • Limit prolonged periods of irrigation – do not water in the evening
  • Avoid nitrogen deficiency – fertilize your lawn in the fall and spring and a healthy fertility program

After this 2023 lawn care season, the properties I treated that had no or little red thread were treated with the following:

  • A late fall application of a high nitrogen and potassium fertilizer in 2022
  • A bridge (hybrid organic) fertilizer (16-2-3) at 4 lbs per 1,000 sq. ft. in early April. This contains biosolids, poultry manure, slow-release nitrogen, and sulfate of potash.
  • A “duration” fertilizer (30-0-5) at 6 lbs. per 1,000 sq. ft. in the middle of May.
  • Each round gets liquid nutrition – Kelp4Less Green Lawn & Turf with liquid yucca and other micros such as molasses, mycorrhizae, and calcium.

This winning formula yielded approximately one pound of nitrogen per 1,000 sq. ft. the previous winter and 2.5 pounds per 1,000 sq. ft. in the spring. The nice part of duration is that high-nitrogen is timed-release in 30, 60, and 90 day intervals.

Chemical

What causes red thread fungus?

Red thread is considered a low-nitrogen disease. It develops in the spring and fall when there’s heavy rain, minimal sunlight, and prolonged leaf blade wetness.

Can grass recover from red thread?

Yes. With proper mowing and nutrition, red thread on most residential lawns will recovery without serious injury.

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Author's Note: this piece has been updated for accuracy since its first publication on

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Author: Mark Marino
My name is Mark Marino, and I am the founder, owner, and operator of Lawn Phix. With a passion for lawn care and turf nutrition for over a decade, I've dedicated countless hours to correcting soil and perfecting lawns. Today, my expertise, backed by formal courses at UMass Extension Pesticide Education, allows me to offer top-tier lawn care services and advice. I am a fully licensed and insured lawn care applicator in Massachusetts, specializing in comprehensive turf nutrition, weed control, and lawn pest control. My license number is AL-0053865. Contact me at [email protected] or +1 (508) 500-8402.

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