Red Thread - fungal disease of lawns and grasses

What causes Red Thread Disease?

As its name suggests, Red Thread causes red / pinkish threads to appear on the lawn. These threads are caused by a fungus - Laetisaria fuciformis / Corticium fuciforme and they grown on infected blades of grass. The threads can extend to around an inch past the height of the grass. Red thread does not always kill off the grass although once infected a blade of grass can be killed off in a couple of days.

The seasons when Red Thread occur are spring and autumn when the climatic conditions are suitable for the growth and dispersal of the fungus - when temperatures are around 16-24 °C. Laetisaria fuciformis may survive dry conditions over winter and summer for up to 2 years.

What are the effects on the grass and lawn?

The infected grass will firstly be 'bleached' in colour, the grass will turn pale cream / white. Not all grass blades will be affected, as non-infected blades may exist next to infected blades. In these circumstances the grass will appear visibly messy. In moist conditions the fungus will form the pink branching threads. Once the threads are well developed the lawn will have reddish / pinkish tinge to it in small patches, these patches may join together to form larger patches.

Maintaining the lawn to prevent the onset of Red Thread

Lawns and grasses that are lacking in Nitrogen are much more susceptible to the onset of Red Thread so feed the lawn when necessary.

To help lawn drainage and aeration (letting oxygen in and carbon dioxide out) aerate the lawn using a hollow spike lawn aerator in autumn.

Use a lawn scarifier or spring tine rake to remove layers of thatch that can 'suffocate' the living grasses.

Ensure the lawn is adequately drained to prevent high moisture levels that fungi will thrive on.

Examine the shadows cast by trees and shrubs and see if they may be contributing to damp lawn conditions, if they are then consider either removing the offending plant or thinning its branches down by careful pruning to let more sunlight through.

How can I help prevent the spread of Red Thread?

Red Thread can be the transportation of infected grass blades and the actual threads themselves thus spreading the infection to uninfected areas of the lawn. The threads and infected grass can be transported by various actions including use of the lawn mower, walking on the grass, high winds etc. Try mowing the infected area seperately from the rest of the lawn and burning the grass clippings that you collect from the infected area.

The fungus that causes Red Thread also produces spores that will promote the dispersal of the disease.

You may want to use a fungicide that contains benomyl or carbendazim to remove the fungal infection. Always double check and precisely follow the manufacturers instructions when using fungicides.