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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  • European pear rust. Image: RHS, Horticultural Science

    Pear rust

    European pear rust is a fungal disease of pears, causing bright orange spots on the leaves. It also affects junipers, causing perennial canker-like swellings on the branches.

  • Pelargonium rust. Image: RHS, Horticultural Science

    Pelargonium rust

    Pelargonium rust is a fungal disease of zonal pelargoniums causing small yellow spots on the upper leaf surface and dark brown pustules on the lower surface. In severe cases affected leaves turn yellow and fall.

  • Pelargonium viruses

    Pelargonium viruses

    Several viruses occur in the UK that can infect and cause a range of symptoms in pelargoniums (also referred to as geraniums).

  • ©RHS WSY0002831

    Pendulous sedge

    Pendulous sedge (Carex pendula) has attractive, green strap-like leaves. It seeds freely and can become a troublesome weed in damp gardens.

  • Peony wilt. Image: RHS, Horticultural Science

    Peony wilt

    Peony wilt is a fungal infection of the leaves and stems of peonies, including tree peonies, causing the foliage to collapse and flowers to die before opening.

  • Guignardia philoprina

    Phyllosticta leaf spot and dieback

    Phyllosticta species are found quite commonly on fallen, dead leaves of a range of woody plants. In some cases they may reside within living leaves and wood without causing problems. Less frequently, they have been associated with leaf spotting and shoot dieback of plants such as holly, rhododendron and yew.

  • A beech tree infected with Phytophthora kernoviae. Image: Forest Research

    Phytophthora bleeding canker

    Bleeding cankers are infections of the bark of trees, including horse chestnuts, by various species of Phytophthora. Infection causes cankers (bark infections) which bleed a dark or reddish- brown sticky fluid.

  • Phytophthora ramorum on rhododendron at Wisley. Image: RHS

    Phytophthora ramorum and P. kernoviae

    Phytophthora ramorum, also known as ramorum dieback or sudden oak death, has caused the death of large numbers of native American oak (Quercus) species and tanoak (Lithocarpus densiflorus) in parts of America. In the UK, P. ramorum is found more commonly on shrubs such as Rhododendron and Viburnum, where it may cause browning of leaves, lesions or cankers, wilting and dieback. The closely-related P. kernoviae causes similar symptoms to P. ramorum.

  • Phytophthora root rot on Wisteria

    Phytophthora root rot

    After honey fungus, Phytophthora root rot is the most common cause of root and stem base decay of a wide range of trees and shrubs. There are a number of different Phytophthora species, all causing very similar symptoms.  Herbaceous perennials, bedding plants, pot plants and even bulbs can be affected, in addition to woody plants.

  • ©RHS_SCN0000548

    Phytophthora: managing outbreaks

    Phytophthora root rot can cause heavy losses in a garden, but there are steps you can take to limit its impact. Here we explore the options available and how best to implement these measures in your garden.

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