You must act quickly when you notice them. Red thread is a disease that causes brown spots in your lawn. On close inspection you will see pink or red filaments on the brown blades of grass. The disease can spread quickly, but the cure is simple. Apply a nitrogen fertilizer to the lawn.
Ammonium sulfate is inexpensive and effective.
Rust is also common during the cool seasons. Rust can turn large areas of your lawn yellow or orange. Rub the grass with your fingers or a white cloth. The orange fungal spores will rub off. Rust is also easily cured by fertilizing.