Red Thread

Red Thread is one of the most common diseases, causing brown patches during warm and wet conditions. It is caused by the fungus Laetisaria fuciformis, and is most common in late summer and autumn. 

Irregular patches of grass take on a reddish tinge that then become light brown or bleached in appearance. On closer inspection, small needle-like growths (stromata) may be seen standing up from the leaves of the grass and can survive in the soil for up to two years. Red thread typically develops on lawns which are poorly aerated and deficient in nitrogen.

Infection occurs during periods of prolonged dampness, so red thread is often a problem in wet humid summers and in autumn when the grass has a heavier dew. The patches can be misleading, giving the impression that the lawn is suffering from a lack of water. Watering the lawn, especially in the evening, exacerbates the problem. 

The fungus does not affect the roots of the grass and recovery may occur after a few days or a few weeks. Red thread will rarely kill the grass, and good lawn care is the secret to avoiding and curing the problem. An application of nitrogen and potassium is often sufficient to control it, but care needs to be taken with applications in late autumn to avoid the production of new soft growth, which may become prone to other diseases. 

In terms of prevention, scarifying the lawn will remove thatch and increase aeration. Poor drainage and compacted areas should be aerated by forking or the use of an aerator. It is important to ensure the soil is not deficient in nitrogen and trace elements, a liquid seaweed should be applied regularly.