Diseases generally affect the grass at times of stress e.g. dry conditions, over watering and high humidity.
Grass will become susceptible to disease caused by fungus which attacks the grass and deprives it of nutrients. Common diseases are Red Thread, Fusarium Patch, Lawn Rust, Dollar Spot and Brown Patch. Domestic lawns are usually only affected by Red Thread and Fusarium Patch the other diseases tend to affect the finer more cultivated grasses not usually found in domestic lawns.