Lawn fungus? - Knowledgebase Question

Lakewood, Co
Question by murarishrest
March 15, 2010
I have circular patches (like big doighnuts) in my lawn where the grass is dead. I was told it was a fungus problem. How can I treat it?

Answer from NGA
March 15, 2010


What you describe sounds like Rhizoctonia Yellow Patch which is sometimes called Frog's Eye. It is caused by the fungus Rhizoctonia cerealis and is favored by cool, wet weather. Early symptoms are 2-3 inch patches of light green to yellow green grass. These areas soon turn light tan or brown and may increase up to 2 feet in size. A "frog-eye" symptom is common, with yellow-green to brown grass surrounding green centers. The patches may have a sunken appearance due to thatch decomposition. Leaf blades near the margin of the patch may have a reddish to reddish-purple tint beginning at the leaf tip and continuing downward. Tan spots with dark borders may develop on the blades prior to complete blighting. Treatment is to dethatch the lawn vigorously. The thatch is how the fungus spreads. You can try adding a fungicide as well, but it will not help without dethatching regularly. Also, lower the amount of nitrogen fertilizer that you give the lawn. Even with dethatching and proper care, it may take up to 2 years for this lawn disease to come under control.

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