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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  • Reversion


    Reversion is the name given when a cultivar known for a particular leaf shape, colour, or other striking characteristic ‘reverts’ back to a different form found in the plant’s parentage. The term is often used to describe a variegated shrub or tree that produces non-variegated shoots.

  • Rhododendron diseases

    Rhododendron diseases

    Rhododendrons (including deciduous azaleas) may be attacked by several diseases, causing unsightly foliage or a lack of flowers. The most significant are powdery mildew and bud blast.

  • ©RHS SCN0006716


    Ring barking or girdling can cause dieback or death of a tree. Damage may result from careless use of machinery close to a tree, excessively tight wire or tree ties or mammals gnawing on the bark, often at the base of the main trunk. Occasionally, girdled trunks or limbs can be saved.

  • Robinia psuedoacacia 'Frisia' with unknown dieback problems.

    Robinia pseudoacacia ‘Frisia’ problems

    Robinia pseudoacacia 'Frisia' is a popular yellow-leaved tree, widely grown in many gardens and public spaces. However, in recent years, this particular cultivar, 'Frisia', has suffered from a range of problems, causing the ultimate loss of the tree.

  • Rose black spot. Image: RHS/Tim Sandall

    Rose black spot

    Rose black spot is a fungal disease of roses where purple or black spots develop on leaves, which often drop early.

  • Well established rose

    Rose dieback

    On a rich soil and with good preparation most roses grow away strongly after planting (as shown here). However, shoot and branch dieback is not an uncommon sight on roses. Weather conditions, poor care and cultivation, diseases or any combination of these can be responsible.

  • Rose powdery mildew

    Rose powdery mildew

    Powdery mildew is one of the most common foliar diseases of roses. The white, powdery fungal growth can be very disfiguring, with repeated heavy infection reducing plant vigour. Cultural techniques play an important role in minimising outbreaks, and fungicides can also be used.

  • Rose problems: frequently asked questions

    Rose problems: frequently asked questions

    Roses seem to suffer from more than their fair share of problems. It is probably partly because this much-loved plant is so widely grown, often in formal rose borders or gardens, and any pest, disease or other problem is soon noticed. That said, some of the older varieties in particular can be very prone to foliar diseases.

  • Rose rust

    Rose rust

    Rose rust is a fungal disease of roses, producing orange or black spore pustules on the undersides of leaves, and orange pustules on distorted stems.

  • ©RHS RHS0005224

    Rosebay willowherb

    The tall, pretty pink flower spikes of rosebay willowherb (Chamaenerion angustifolium) are a common sight on railway banks and disturbed woodland. It is a useful nectar source for pollinators but self-seeds readily making it a troublesome garden weed.

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