Grasses in the lawn, just like many other garden plants, are subject to a number of disease problems. Luckily, they rarely do severe damage. The best way to control them is to ensure the grass is strong and healthy.
The commonest lawn diseases are listed below.
Red thread is one of the commonest fungal diseases on lawns, especially on lawns that are deficient in nitrogen. It produces brown patches, especially during a wet summer and during the autumn.
Red thread is caused by the fungus Laetisaria fuciformis. It rarely completely kills the grass and the patches recover with proper lawn preparation and treatment. Affected grass produces a reddish tinge, later becoming light brown or even bleached in appearance and the leaves may bind together. Patches vary in size, usually from 7.5 to 25cm (3 to 10in) in diameter, but can be much larger.
Fusarium patch, more commonly called snow mould, is a common cause of brown patches on lawns. It is particularly prevalent in autumn or during mild spells in winter, but attacks can occur at any time of the year.
Snow mould is caused by the fungus Monographella nivalis and at first produces small patches of yellowy, dying grass that usually turn brown later. The patches increase in size and may reach 30cm (12in) in diameter, sometimes merging so that large areas can be affected. During wet conditions a white or pinky, cotton-like fungal growth may be noticed, especially at the margins of the patch.
Fairy rings are caused by a number of different fungi that produce rings of dead grass and usually toadstools in the lawn in late summer and autumn.
Symptoms of attack are variable, depending on the fungus responsible, but the following are characteristic of fairy rings: an irregular ring of dead grass; adjacent to the dead grass, on both the outside and the inside of the ring, the grass may be greener than the rest of the lawn.
It is always worth kicking over the toadstools before they mature and release spores. But if you’re patient, as the rings grow in size each year, eventually they will outgrow the lawn!
Take-all patch is one of the most damaging lawn diseases, but thankfully it is not that common. It first appears in mid-summer.
Take-all patch is caused by the fungus Gaeumannomyces graminis, formerly known as Ophiobolus graminis - hence its former common name of ophiobolus patch. It first appears as small circular patches, expanding to around 50 to 100cm (20 to 40in) in diameter. It tends to affect bent and other fine-leaved grasses producing dying areas of straw-coloured grass. Take-all patch eventually disappears after December, but can keep coming back for several years.
It is fairly easy to keep lawn diseases under control or prevent them from occurring in the first place by practicing good lawn care.