Mushroom Half-Circle Killing St. Augustine: Fairy Ring or Fungus?

St. Augustine lawn: mushrooms formed half-circle, grass died inside. Mushrooms expanded outward, grass kept dying. Large dead area now. Cause and cure?

Two Possibilities

1. Fairy ring (Type I): Hydrophobic fungal mat repels water → grass dies from drought. Mushrooms at leading edge. Grass inside ring often greener (nutrient release)—but not always.
2. Pathogenic fungus + mushrooms: Overwatering fueled a disease (brown patch, take-all) killing grass; mushrooms are secondary decomposers.

Diagnose & Act

• Check soil moisture in dead zone vs. green: hydrophobic = fairy ring.
• If fairy ring: core aerate heavily, apply wetting agent, fertilize to mask symptoms. No reliable cure.
• If disease: stop night watering, apply labeled fungicide, improve drainage.

Mushrooms are the fruit; the problem is underground. Target the cause, not the caps.