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This is an image of Red Thread

Red Thread… Not The Type Your Clothes Are Made With

What is Red Thread?
Red Thread disease is caused by the fungus Laetisaria fuciformis. It appears during rainy periods in late spring and early summer. Red thread is usually associated with perennial ryegrass, fine fescue and Kentucky bluegrass lawns that do not receive sufficient amounts of nitrogen. Red thread disease is usually restricted to leaf sheaths, leaves and stems of turfgrasses; in severe cases may kill the entire plant. 

What does Red Thread look like?
Red thread disease symptoms appear as circular or irregularly shaped patches of blighted turf, typically with a pink or red cast.The turfgrass disease resembles similar symptoms to pink snow mold, pink patch disease, and dollar spot. You can easily tell them apart by the pinkish-red, antler-like threads (known as sclerotia) that protrude from the tips of infected grass blades.  In the advanced stages, leaves become covered with bright red thread-like strands of fungal mycelium at the tips of the affected leaves. Sclerotia are sometimes accompanied by pink, web-like mycelium when conditions are wet and humid. Eventually diseased plants dry out and fade to a bleached straw color. The stringy sclerotia coupled with the fuzzy mycelium is what earns the disease its memorable name (and makes your lawn look like it’s having a bad hair day). 

This is a closeup image of Red Thread


What causes Red Thread?
Red Thread becomes dormant mycelium on dead leaves and stems of previously infected plants in the winter. The mycelium resumes growth when warmer temperatures and sufficient moisture returns in spring. The fungus enters grass leaves through cut tips or natural openings and spreads rapidly through the rest of the foliar portion of the plant. Mycelium on infected plants can be broken loose and transported by foot traffic and mowers to other plants. Red thread tends to develop when air temperatures are 65° to 75°F, with prolonged periods of humid or rainy weather in late spring through early summer. Occasionally, the disease occurs in warmer, drier weather. Red thread frequently occurs with another disease, pink patch. Both pink patch and red thread have similar symptoms. Both diseases also develop under the same environmental conditions and control measures are similar for both as well. Overall what can cause red thread would be:

  • Air temperatures between 40 and 75 °F. 
  • Red thread can occur at any time of year, but is most severe in the spring and fall when conditions are wet and cool.
  • Drought.
  • Low fertilization.
  • Slow-growing lawns (highly susceptible to the disease).
  • Poor access to sunlight.
  • Excessive thatch (can hold disease).
  • High humidity and excessive moisture.

Control Measures
It is possible turf affected by red thread will recover within a few weeks, but lawns planted to highly susceptible cultivars of perennial ryegrass, kentucky bluegrass or fine fescues can sustain severe damage. Fungicides are available to treat the fungus but there are other measures you can take as well.  If you don’t prioritize lawn care maintenance, the disease is more likely to return. 

Some cultural measures you could implement would be:

  • Limit heavy traffic on the lawn.
  • Water less often and for longer periods as it  promotes a strong root system.
  • Increase access to sunlight by trimming shrubs and trees. 
  • Collect grass clippings after each mow so that the disease doesn’t spread.
  • Aerate (liquid or mechanical). When soil is compact, the lawn’s root system has little access to air, oxygen, and nutrients. Relieving compact soil will help improve your lawn’s growth and also improve drainage.
  • Dethatch the lawn
  • Watering at the right time of day. Water the grass in the early morning before 10 a.m. so the lawn has enough time to absorb the moisture before the water evaporates from the afternoon sun. Avoid nighttime watering; otherwise, you will create a moist environment that encourages disease and pests. 
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