Red Thread
Laetisaria fuciformis
Red thread is a fungal turf disease causing pink-red patches with needle-like fungal threads, common in cool, humid, low-nitrogen conditions.
Red thread is caused by the fungus Laetisaria fuciformis, which attacks the leaf blades of many turfgrass species without generally killing the crown or roots. The most distinctive feature is the fungal growth itself: fine, coral-pink to red, needle-like or antler-shaped strands (sclerotia-like structures) that extend from the tips of infected leaves, especially visible in early morning when dew is present. Under humid conditions these threads can appear as a fluffy, cottony pink-red mycelium binding leaf blades together.
Affected turf shows irregular patches ranging from a few centimetres to half a metre or more across, typically pink, red or bleached tan in colour, which can merge to form larger irregular areas across a lawn or sports surface.
The disease is favoured by prolonged leaf wetness, humid weather, cool to mild temperatures (roughly 15–25°C), and low nitrogen fertility. It is common in Australia during autumn and spring in temperate regions, and can also occur in cooler, wetter periods in subtropical and cool-season turf areas. Fine fescues, perennial ryegrass and some couch cultivars are particularly susceptible.
Management relies on cultural practices rather than curative treatment alone: improving nitrogen nutrition where deficient, reducing leaf wetness duration through better drainage, airflow and irrigation timing (avoiding evening watering), removing excess thatch, and mowing with sharp blades to reduce leaf tearing. Collecting and disposing of clippings during active outbreaks can reduce spread, as the fungus survives in infected leaf debris and thatch.
How to identify
- Irregular pink, red or light tan patches in turf, from a few centimetres to large diffuse areas
- Leaf blades appear water-soaked, then bleached or straw-coloured as they die back from the tip
- Fine, needle-like or antler-shaped pink-red fungal strands protruding from leaf tips, most visible in early morning dew or after rain
- A cottony, pink-tinged mycelium may bind leaf blades together in humid conditions
- Turf usually recovers from the crown once conditions dry out, distinguishing it from diseases that kill the crown or roots
Field check: Inspect affected patches closely, or with a hand lens, in the early morning while dew is present — the red, thread-like fungal structures on leaf tips are diagnostic and not present in most lookalike problems.
Lookalikes: Dollar spot produces small, sunken, straw-coloured patches (often coin-sized) with hourglass-shaped lesions on individual leaves but lacks the red thread-like growths. Pink patch, a related disease, produces similar pink patches but without the distinctive needle-like red threads, instead showing a more gelatinous pink fungal growth on leaf sheaths.
