Q What is red thread?

A Red thread is a turf disease that affects grass leaves, caused by the fungus Laetisaria fuciformis.

Caption:  Red thread causes patches of dead grass

Q How do I recognise it?

A It appears as patches of dying grass, up to 1m across, often with a red tinge. The disease starts at the leaf tips, which turn pale brown, then moves downwards. On closer examination, pinky red threadlike structures can be seen among the leaves. These are the fungal growths.

Q Could I mistake it for anything else?

A Dead patches in lawns can have many causes. With this disease, the red threads are a clear diagnostic feature.

Q What damage does it do?

A Red thread attacks the leaves and occasionally the roots of the grass, but once the disease is brought under control the lawn should recover.

Q What is its life cycle?

A The fungal threads produce coral-red, needle-like outgrowths, 1-2mm long, known as stromata. These can remain dormant in the soil for up to two years before germinating to reinfect the grass. Both these and the fungal threads are easily carried by water, shoes and lawnmowers, thus spreading the disease.

Q When do attacks occur?

A Red thread tends to appear in late summer, in wet or humid conditions, and can affect many lawn grass species.

Q How do I control an attack?

A Red thread tends to affect grass that is short of nutrients, so simply adding nitrogen may do the trick. However, it is not advisable to do this later than August as the soft, new growth produced may then fall prey to autumn fungal problems. The alternative is to use the fungicide trifloxystrobin, available as Lawn Disease Control from Bayer Garden. Improved maintenance is the only organic treatment.

Q How do I prevent it in future?

A It thrives on impoverished soils, so building up soil fertility will help to prevent it. Good general maintenance will also increase the lawn’s resistance to fungal attack.