Pythium Blight Lawn Disease

Identification: Pythium Blight first appears as water-soaked, slimy/greasy, dark spots on the lawn. These patches can be anywhere from 1 - 12 inches in diameter. From there, it progresses until the leaves of the affected grass shrivel and change color from green to a light brown. Another key feature in identifying this disease is the appearance of cottony, cobweb-like growth on the affected areas, especially during the early mornings or night.

Cause: The onset of this disease can be caused by several factors, including over-fertilization, particularly wet/moist conditions, improper thatch control, and high temperatures. In general, this disease is most severe when day temperatures are around 84-95 degrees, night temperatures remain above 68 degrees, and there is a lot of moisture in the area. Water drainage paths can spread the disease as can mowing a lawn when it is wet.

Prevention: There are several things you can do to prevent this disease from affecting your lawn. These include:

  • Good water management, don't water too much or too late in the day
  • Remove excess thatch build-up
  • Avoid over-fertilization
  • Improve air circulation and drainage of the lawn
  • Increase the mowing height to promote root growth
  • Apply preventative fungicides if conditions are likely to favor the disease

Treatment: There are several fungicides that can help treat and/or prevent this disease,. These should be applied whenever the conditions are favorable for the appearance of Pythium or when the first signs of the disease is detected. It is also recommended that, 7 - 21 days after planting, you treat the new growth with fungicides to prevent infection early on.

Grass Types Susceptible: All grass types are susceptible to Pythium Blight though the following are particularly so:

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