Red thread is one of the most common fungal patch diseases found on lawns, particularly where the turf is deficient in nitrogen. It causes brown patches of turf, especially during a wet summer.
Red thread is a common cause of patches of dead grass on lawns during wet summers and in autumn. It is caused by the fungus Laetisaria fuciformis. Red thread will rarely kill the grass completely, and the patches will recover with appropriate remedial action. The disease can develop at any time of year, but is most common in late summer and autumn.
You may see the following symptoms:
- Patches of affected grass with a reddish tinge at first, later becoming light brown or almost bleached in appearance
- Patches usually vary in size from 7.5cm (3in) to 25cm (10in) in diameter, but can be much larger
Two types of fungal growth may be seen on the patches, particularly under wet or humid conditions. Both are visible to the naked eye, but are seen better with a hand lens or magnifying glass.
- The first takes the form of small, pink, cottony flocks, and can be confused with growth of the fungus causing snow mould
- The second is specific to red thread, and gives the disease its common name. Pinkish-red, gelatinous, thread-like structures (stromata), 1-2mm (less than ¼in) in length, are produced on the leaves and may bind them together
If red thread appears, application of nitrogen to the affected area will often be sufficient to control it. Nitrogen is best given as sulphate of ammonia at 15g per sq m (½oz per sq yd). Do not apply after August to avoid the production of soft growth which is prone to snow mould.
The threat from red thread can be reduced by taking action to improve the drainage and aeration of the turf. Scarifying will remove thatch and moss and increase aeration. Poor drainage and compacted areas can be alleviated by the use of a solid-tine or hollow-tine aerator. Ensure that the soil is not deficient in nitrogen. Disposing of (not composting) grass clippings will reduce the amount of fungus present to re-infect the lawn.