Brown Patch Disease in Lawns

Brown patch is the most widespread fungal disease of turfgrass in the eastern United States. It is caused by Rhizoctonia solani, a soil-borne pathogen that is present in virtually every lawn — it only becomes destructive

Brown patch is the most widespread fungal disease of turfgrass in the eastern United States. It is caused by Rhizoctonia solani, a soil-borne pathogen that is present in virtually every lawn — it only becomes destructive when temperature and humidity conditions combine to trigger an outbreak. Understanding those conditions is the key to both prevention and timing any treatment.

Identifying brown patch

Per Penn State Extension's turfgrass disease guide, brown patch appears as roughly circular patches of blighted turf ranging from a few inches to several feet in diameter. In morning dew conditions, look for a dark "smoke ring" — a ring of darker, water-soaked grass at the advancing edge of the patch. This ring disappears as the dew dries.

Individual infected blades show a characteristic symptom: a tan lesion with an irregular brown border, sometimes described as having a "chocolate brown" margin on a light tan center. The blade dies back from the tip.

Cool-season vs. warm-season susceptibility

Per NC State Extension TurfFiles, susceptibility differs by species:

Highly susceptible cool-season species:

• Tall fescue (Festuca arundinacea) — the most severely affected cool-season species; can see complete patch death
• Perennial ryegrass (Lolium perenne)

Moderately susceptible:

• Kentucky bluegrass (Poa pratensis) — can develop brown patch but typically less severe; often recovers more quickly

Susceptible warm-season species:

• Zoysiagrass (Zoysia japonica) — "large patch" disease is a related Rhizoctonia disease in warm-season grasses; see below
• St. Augustinegrass — susceptible to a related form

Fine fescues and creeping bentgrass are also susceptible but in different temperature ranges.

Important distinction: In warm-season grasses, Rhizoctonia causes "Large Patch" (formerly called Zoysia patch or brown patch of warm-season grasses), which has different temperature requirements — it occurs when soil temperatures fall in the 50—70°F range (spring and fall), not in summer heat. Per NC State Extension, large patch on zoysiagrass is primarily a fall disease in the Carolinas and Mid-Atlantic.