Observe the Infected Area
Get down on your hands and knees and examine the damaged lawn area. Inspect for the presence of insects or damage caused by herbicides, equipment leaks or animals including pets. Make notes by answering the following questions:
What kind of grass do you have (many parasitic fungi are specific to certain types of grass)?
What time of year is it?
When did the damage first appear?
Does the damaged grass appear greasy or water-soaked?
Are there any visible fungal structures (red threads, rusty spots, smoky haze appearing in the morning, etc.)?
When did you last fertilize the grass?
How long and how often is the lawn being watered?
How much sunlight does the area receive (full day, half-day or less)?
How does air circulate in the area? Do trees and shrubs surround the damaged lawn?
Is the damaged area higher than, lower than, or at the same level as the surrounding lawn?
What shape and size is the damaged area? Is it growing?
Are there any differences in the lawn's color around the damaged area?