Rust Fungus
Rust fungus in lawns is caused by the fungus Puccinia graminis. It causes white and yellow spots on grass leaves. It spreads through millions of microscopic spores, which can resemble rust or dust if they get on your shoes and pants. It can spread throughout your lawn when the spores are blown by the wind or are scattered by a dog.
Issues
Rust fungus rarely kills a healthy lawn, although it can detract from its appearance. If your dog plays in the yard, it can pick up rust spores on its fur and spread it to uninfected areas of grass. If your dog roams the neighborhood, it can spread the infection to other lawns.
Solutions
You can control rust fungus by improving air circulation around infected areas. Keep your dog out of problem areas in your lawn to prevent reinfection. Watering deeply, mowing your lawn frequently and removing all grass clipping will help bring the infection under control.