Though St. Augustine grass makes a beautiful, lush lawn with a thick and luxurious carpet when painstakingly babied, this type of grass is highly susceptible to many invaders and pests, including viruses and fungal enemies that lead to unattractive grass disease. Learning to recognize the symptoms of grass disease in a St. Augustine lawn is the first step toward controlling the problem.
Circular Brown Patches on St. Augustine
Brown patches ranging from a few inches to several yards in diameter indicate a problem with brown patch grass disease. Brown patch disease is commonly caused by a fungus that infects in cool, wet lawn soil conditions. One distinct feature of brown patch grass disease is a gray ring around the brown patches, a symptom most visible in freshly cut St. Augustine grass. Nematodes and chinch bugs may also cause circular brown patches on St. Augustine grass, but these patches will lack the defining gray ring. Brown patch is one of the most common diseases in St. Augustine lawns.
Small, Dead, Discolored Lawn Spots
Smaller circular spots no larger than the size of a tea saucer may indicate a problem with dollar spot grass disease. A distinct feature of dollar spot grass disease is a fuzzy, weblike material that is most visible in the morning dew.
Diffuse Patches of Dying Grass
Lawns exhibiting widespread patches of yellowing, dying grass may be experiencing take-all root rot. Take-all root rot is caused by the fungus Gaeumannomyces graminis var. graminis and can kill an entire St. Augustine grass lawn. Though this disease can attack even a healthy St. Augustine lawn, take-all root rot is most common on lawns that have been overfertilized, particularly with lime or nitrogen.
Slowly Progressing Yellowing
A St. Augustine lawn that experiences a slow yellowing decline over several years may have become infected with the virus that causes St. Augustine Decline (SAD). This virus usually weakens St. Augustine grass enough for invading grass weeds to take hold in the weak patches of the lawn. It is characterized by yellow mottling on the grass blades that slowly progresses to encompass the entire blade. SAD is spread by lawnmowers which have become contaminated with the disease, most commonly lawnmowers owned by gardeners who tend several lawns.