Brown Patch: Cool Season Disease of St Augustine Turf
Brown patch is a cool-season disease that forms tannish circles or joined lobed circles. Brown patch is more of a cosmetic problem than lethal. It does not kill the turfgrass plant, it only affects the leaves, and the lawn will recover. The fungus that causes brown patch is a beneficial part of the turf ecosystem for recycling organic matter and cannot be eradicated.
How to Identify Brown Patch
Brown patch is most active during the cooler temperatures of fall and spring. Brown Patch forms circles and/or lobed circles of tan/green weak turf. The rings start out fist size and can grow to be 20 feet in diameter or larger. The outer edge of the ring (active area) is often yellow in color. The disease is only active when temperature, wind, light, and moisture are perfect – as soon as any of those conditions change, the fungus will become inactive. Many lawns are not affected by brown patch, and others have chronic problems with brown patch.
What to Know about Brown Patch?
- Brown patch generally will not kill your grass – unless it is near death, to begin with.
- Brown patch is a temporary condition – brown patch will cease when conditions change.
- The lawn will recover and return to its natural beauty.
- The causal agent is part of the environment – it is a soil-born fungus and cannot be eliminated.
Brown Patch can be controlled with good cultural practices!
Warning: Do not apply nitrogen fertilizers to a lawn with brown patch in hopes of curing the disease, it will make the disease worse. Brown Patch responds to excess nitrogen by getting worse. The addition of potassium applied to the lawn before the cool weather can reduce the severity and occurrence of brown patch.
To reduce the impact of Brown Patch during the cool season months, I use slow-release organic sources for nitrogen in very sparse amounts and high amounts of potassium all year long to keep nitrogen levels low and potassium levels high.
In severe cases, I will use a commercially available fungicide as a curative measure. However, fungicides are temporary only lasting for 2 – 3 weeks. Retreating the lawn will be necessary when conditions are perfect for brown patch to become active.