Why has my lawn gone pink and reddish in patches?

Red thread is the most common lawn disease in Britain and the least alarming. It appears from late spring through autumn, especially after warm humid spells, and it is strongly associated with low nitrogen. Fine fescue-rich lawns get it worst. The fungus attacks the leaf, not the crown or root, so the grass regrows from the base once conditions change.

What you'll need

• Balanced lawn feed
• A rake (optional)

Step by step

1. Confirm it by looking closely at the leaf tips.Get down and look. Red thread shows tiny pink to red needle-like threads projecting from the leaf tips, and sometimes pink cottony webbing in the morning dew. Nothing else in a UK lawn looks like that.
2. Check the patches are straw-coloured rather than dead.Irregular bleached or tan patches from a few centimetres to about 25cm across, with green grass mixed through them. If the whole patch is dead down to the crown, look at drought, grubs or urine instead.
3. Ask when the lawn was last fed.Red thread is a nitrogen indicator. A lawn that has not been fed for a couple of years, or a new lawn on poor subsoil, is the classic case.
4. Apply a balanced lawn feed.A spring or summer lawn feed in the growing season. The grass grows away from the infected leaf and the patches fade in two to four weeks. Water it in if rain is not forecast.
5. Mow and box the clippings while it is active.Boxing removes infected leaf tissue rather than redistributing it. Return to leaving clippings once it has cleared.
6. Improve air movement and reduce surface wetness.Long humid periods with dew sitting on the leaf all morning favour it. Aerating, avoiding evening watering and not over-boxing a shaded, sheltered lawn all help slightly.
7. Do not reach for a fungicide.Domestic lawn fungicides are largely unavailable to householders in the UK now, and red thread does not warrant one anyway. It is a feeding problem wearing a fungal costume.
8. Overseed with a ryegrass-rich mix if it recurs badly.Fine fescues are the most susceptible. A more ryegrass-based mixture is noticeably more resistant on a family lawn.

Tips

• Red thread on a brand new lawn is normal and usually means the topsoil was thin. Feed it and it settles down within a season.
• It is not harmful to pets or people, and it does not spread to garden plants.
• If a lawn has red thread and moss and thin growth together, the honest diagnosis is a hungry, compacted lawn rather than three separate problems.

Common mistakes

• Treating it as a serious turf disease — It affects leaf, not crown. The grass recovers. Panic responses like heavy fungicide or stripping the turf out are entirely disproportionate.
• Feeding heavily in late autumn to fix it — A high-nitrogen feed going into winter produces soft growth that then gets fusarium, which is a considerably worse disease. Feed for red thread in the growing season only.
• Watering in the evening through a humid spell — It extends the hours the leaf stays wet, which is precisely the condition the fungus needs.

If it doesn't work

Questions people ask