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.
Fungus and Disease Articles
Small brown to tan or straw-colored spots in your St Augustine grass lawn is Dollar Spot. They can be a few or many and make the lawn appear blotchy or spotted.
Sugarcane Mosaic Virus (SMV) attacks St Augustine turf grass lawns in Pinellas County, FL APL Lawn Spraying treats lawns with Sugarcane Mosaic Virus.
What are those circular patches of dead grass in St Augustine turf grass lawn? Most likely it is Brown Patch - a cool weather fungus.
Fairy Rings are those dark green circles in the lawn with large white mushrooms growing along the outer edge.
Brown Patch is a cool weather fungus that when conditions are perfect, can cause cosmetic damage but not kill St Augustine turf grass lawns.