Brown patch
A lawn fungus that creates large circular brown or yellow patches in warm, humid weather, often with a darker ring at the edge.
Also known as: Large patch, Rhizoctonia blight
Symptoms and identification
Circular or irregular patches, from 30 cm to several metres across, turn brown or yellow. A dark grey ring, called a smoke ring, may show at the edge in the early morning. Leaf blades have tan lesions with a dark border, but roots usually survive and the grass can regrow.
Causes
The fungus Rhizoctonia thrives when nights stay warm, above about 20 degrees Celsius, humidity is high and the grass stays wet for long periods. Heavy nitrogen feeding, poor drainage, thatch and watering in the evening raise the risk.
Organic treatment
Reduce watering, avoid feeding with high nitrogen, and remove dew by brushing or mowing in the morning. The lawn usually recovers when conditions cool down.
Prevention
Water early in the morning and no more than needed, avoid heavy nitrogen feeding in hot weather, mow high and improve drainage and air movement. Remove thatch and aerate compacted soil.
Chemical treatment (use with care)
Use a fungicide labelled for brown patch on the lawn as a preventive in warm, humid periods when it has been a problem before, following the label.