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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  • 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.

  • Strawberry viruses

    Strawberry viruses

    Several viruses and phytoplasmas (which have characteristics in common with both viruses and bacteria) infect strawberries to cause a wide range of symptoms which result in poor vigour and low yield.

  • Sweet pea leaf with virus. Image: RHS, Horticultural Science

    Sweet pea viruses

    Many viruses affect Lathyrus spp. (sweet peas) causing streaked flowers, mottled leaves, stunted growth and dead patches on leaves.

  • Take-all patch. Image: STRI

    Take-all patch

    Take-all is a fungal disease of lawns, particularly those with a high percentage of fine bentgrasses (Agrostis spp.). It causes brown patches of grass, most often in summer when the turf is under drought stress.

  • Tar spot of maple

    Tar spot of maple

    Tar spot is a very conspicuous fungal leaf spot disease of sycamore and some other maples. Whilst the large leaf spots sometimes cause gardeners concern, they actually do very little damage to the tree.

  • Fly agaric (Amanita muscaria). Credit: RHS/Herbarium.


    There is no standard definition for a toadstool, and no clear distinction between toadstools and mushrooms. Both terms refer to the fruiting bodies produced by fungi. Most of these fungi are harmless or even beneficial to plants, but there are a few that can cause disease problems, such as honey fungus and the fairy ring fungi.

  • Tomato leaf mould

    Tomato leaf mould

    Leaf mould can develop rapidly to cause significant yield loss in greenhouse-grown tomatoes. It is rarely seen on outdoor crops.

  • Tomato plants affected by virus show mosaic patterns on leaves. Image: RHS, Horticultural Science

    Tomato viruses

    Many viruses affect tomatoes causing mosaic patterns on leaves, leaf distortions, stunted growth, bronzing or marbling patterns on the fruit.

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