Diseases & Disorders

Helpful advice on what to do when problems strike, whether they're diseases, disorders or otherwise - and how to prevent them occurring


Fungal infection

Phytophthora is our second most reported disease. Causing die-back and leaf damage on trees and shrubs and is often fatal.

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  • Sclerotinia disease. Image: RHS, Horticultural Science

    Sclerotinia disease

    Sclerotinia disease is a fungal infection of many vegetables and ornamental plants. The fungus lives for long periods in the soil. When infected, plants rot at the base and a white fluffy mould may grow on affected parts.

  • ©RHS WSYD0012523

    Sheep’s sorrel

    Sheep’s sorrel (Rumex acetosella) is a relative of dock whose tangy young leaves in long grassland are favoured by foragers. However, in gardens especially on sandy, acidic soils it can be a troublesome weed.

  • Silver leaf on plum. Image: RHS, Horticultural Science

    Silver leaf

    Silver leaf is a fungal disease of the wood and leaves of some trees, especially plums, apples, apricots and cherries. The fungus infects the wood through wounds and causes a silvering of the leaves followed by death of the branch.

  • © RHS Science

    Sirococcus blight

    This recently recognised fungal disease affects cedars and hemlocks. It causes shoot tip dieback and defoliation. Young trees may be killed if branches/trunk are girdled but it is reported that infected mature trees can live for many years.

  • Slime mould on a lawn. Image: RHS, Horticultural Science

    Slime moulds on lawns

    Slime moulds occasionally cause concern when they appear on lawns, but they do not attack or kill the grass. They vary greatly in their colour, size and form. Their spore-producing structures are often very fragile, disintegrating when touched.

  • Smuts


    Whilst they are not seen as commonly as their close relatives the rusts, smut fungi can affect a range of garden plants, including some widely-grown vegetables and ornamentals. Some smuts cause conspicuous growth distortions, whilst others cause leaf spotting. All can contaminate the soil for extended periods of time.

  • Grey mould on snowdrops. Image: RHS, Horticultural Science

    Snowdrop grey mould

    Grey mould in snowdrops is an infection or disease caused by the fungus Botrytis galanthina, causing leaves and flowers to collapse. A fuzzy grey mould forms under wet conditions.

  • Sooty blotch and fly speck of apples

    Sooty blotch and fly speck of apples

    These blemish diseases are caused by unrelated fungi, but both result in dark fungal growth on the surface of the fruit. Apples are affected most commonly, but the fungi may also be found on pears, plums and citrus fruit. Eating or cooking quality is not affected. The diseases are most common in wet summers.

  • Sooty mould

    Sooty moulds

    The presence of sooty mould fungi usually indicates that a plant has become affected by a sap-sucking pest. Sooty moulds do not attack the plant directly, but their growth is unsightly and can reduce plant vigour by preventing photosynthesis.

  • Strawberry black eye. Credit: RHS/Tim Sandall.

    Strawberry black eye

    Black eye is the most recognisable form of frost damage on strawberries. Affected flowers will not set fruit.

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