Grass like any other plant may be susceptible to attack by pests and diseases. Grass is more resistant and less prone to disease when it is well maintained and is growing will. But with even the best maintenance regime your lawn may still be open to attack.
Lawn diseases are not something that an amateur gardener should unduly worry about. It is often that case that patches which are caused by over fertilization or weed killer are misdiagnosed as a disease. Below is a list of the common ailments for a lawn.