Lawn diseases

There are four main fungal diseases of lawn grasses.

Take-all patch

Take-all patch (previously called ophiobolus patch) causes circular, brown or straw coloured patches of grass – often extensive in size, up to 1m (3ft). These mainly occur in summer when the grasses are suffering drought stress. It usually attacks fine-leaved grasses. It is one of the most damaging lawn diseases, but it is not that common.

Red thread

Red thread is one of the commonest diseases on lawns. It produces brown patches, and affected grass produces a reddish tinge, later becoming light brown or even bleached. The leaves may bind together. It is more prevalent during a wet summer and during autumn, but attacks can occur at any time of the year, especially on lawns growing on soils that are deficient in nitrogen. Patches vary in size, from 7.5-25cm (3-10in) in diameter, but can be even larger.

Fusarium patch or snow mould

Snow mould, more correctly referred to as fusarium patch, also eventually causes brown patches. These start off as small patches of yellowy, dying grass. The patches increase in size and may reach 30cm (12in) or more in diameter, often merging to produce larger brown areas. During wet conditions a white or pinky, cotton-like fungal growth may be seen, mainly at the margins of the patch.

Fairy rings

The fungi responsible for fairy rings produce rings or circles of dead grass, together with their associated toadstools, in late summer and autumn.

Symptoms are variable, depending on the fungus responsible, but the characteristic symptoms of fairy rings are: an irregular ring of dead grass; adjacent to the dead grass, on both the inside and the outside of the ring, the grass may be greener than the rest of the lawn.

• Lawn grasses

Take-all patch is called by the fungus Gaeumannomyces graminis, previously known as Ophiobolus graminis – hence its former common name of ophiobolus patch. Red thread is caused by Laetisaria fuciformis and fusarium patch by Monographella nivalis. Fairy rings are caused by several different fungal species.

Grass that isn’t growing well, isn’t growing on good soil or is neglected is far more prone to all these fungal diseases. But even well cared for lawns may have an outbreak, especially during adverse or severe weather conditions.

The best way to prevent lawn diseases happening in the first place is to ensure you practice good lawn care.

Mow regularly and at the right height (around 1½in/4cm high for most lawns). Aim to keep the grass at more-or-less this height all year round. Never scalp the lawn, as this weakens the grass.

Ensure the lawn is well fed all year round by using a spring/summer lawn feed in spring and summer. Feed in autumn too, but avoid high nitrogen fertilisers as these produce soft growth more prone to diseases (and frost and waterlogging) – always use an autumn lawn feed instead.

Thatch can encourage lawn diseases, so scarify with a spring-tine rake or electric scarifier in autumn and/or spring to remove thatch, dead moss and any other dead material and help aerate the soil.

Poor drainage and compacted soil will encourage diseases and reduce grass health, so improve drainage by forking the lawn or use a solid-tine or, better still, a hollow-tine aerator in autumn. Then brush in a lawn topdressing.

Dry lawns in summer can be more prone to diseases as it weakens the grass, so wherever possible water thoroughly during extended dry periods.

Disposing of grass cuttings will reduce the amount of fungus present to re-infect the lawn.

When laying a new lawn, pay attention to good soil preparation to prevent the soil becoming compacted (especially on clay soils) or drying out (especially on sandy soils) in the first place.

For fairy rings, it pays to remove the toadstools, as soon as they appear to prevent them spreading their spores. If all else fails, just be patient – the fairy rings grow bigger each year and in time will outgrow the lawn and go next door!

Keep the grasses in the lawn growing as strongly as possible, and lawn diseases will rarely bother your lawn.

• Lawn fertilisers
• Grass seeds
• Lawnmowers
• Lawn scarifiers