Brown patch
Rhizoctonia solaniA fungal disease that causes circular brown patches, often with a darker "smoke ring" edge, in mild, humid weather in spring and autumn.
Lawn Library
Diseases
Lawn diseases: the symptoms, the conditions that favour them, and how to prevent them.
Identify a lawn disease from the symptomsFairy rings
Many fungi (Basidiomycetes)Rings or arcs of darker, faster-growing grass, sometimes with mushrooms or a ring of dead grass, caused by fungi breaking down organic matter in the soil.