Fusarium Blight Lawn Disease

Identification: When first infected by Fusarium Blight, patches of grass from 2 to 6 inches in diameter turn light green. While these areas can be circular in shape, they can also appear as elongated streaks or even crescents. During periods of high temperatures, the areas affected by the disease quickly change color from there initial light green to a reddish brown and, finally, to a tan or straw-colored appearance. During this time, the most obvious symptom to show that it is, in fact, Fusarium is the appearance of a roughly ring-shaped area up to 3 feet in diameter that contains a patch of healthy grass in the center. This gives the affected area a "frog-eye" pattern. As the disease continues and the grass dies, the crown and basal area of the dead grass displays a reddish rot and becomes hard and tough. On an individual level, dark green blotches envelope the full width of the leaf blade and, eventually, these blotches become reddish-brown and then a dull tan.

Cause: While this disease is actually caused by a fungal growth, there are several conditions which favor its appearance and growth. When daytime temperatures reach 70 degrees or higher, this fungus begins to produce spores. As temperatures become 75-90 degrees and there is high humidity, the spore production increases dramatically and can kill infected areas in as little time as 4 to 7 days after the first symptoms appear. When temperatures and/or humidity is low, however, the disease shows very little activity. High nitrogen levels, excess thatch, and excessive watering can also contribute to the appearance and spread of this disease.

Prevention:

  • Remove excess thatch
  • Maintain a regular watering schedule, avoiding frequent, shallow waterings
  • Fertilize your lawn appropriately
  • If you are planning on seeding bluegrass, it is recommended that you add a mixture of 20% perennial ryegrass as well to help prevent this disease
  • Maintain your lawn at the recommended height

Treatment: The only way to treat this disease, beyond stricter maintenance controls or reseeding to repair damage, is to apply fungicides. It is recommended that, if you choose to use a fungicide, that you apply it during the spring before or just after symptoms of Fusarium Blight appear.

Grass Types Susceptible:

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