Fungus and Disease
Brown Patch is a cool weather fungus that when conditions are perfect, can cause cosmetic damage but not kill St Augustine turf grass lawns.
What are those circular patches of dead grass in St Augustine turf grass lawn? Most likely it is Brown Patch - a cool weather fungus.
Mushrooms growing in the lawn does not indicate you have a lawn disease or fungus in your St Augustine grass lawn. It means you have mushrooms.