Research
Phytophthora root diseases
What is Phytophthora?
Phytophthora
is the name of a groups of soil- and water-borne fungi, which
are a common cause of death in a variety of trees and shrubs.
How Phytophthora affects the garden
Introduced to the garden in various ways - on infected plants, in irrigation water, in soil or windblown dust - the fungus may remain dormant in the soil for many years. Most often during wet weather or on poorly drained soils, infection may occur through the roots of susceptible plants, which are killed. The foliage is affected only when the infection is well advanced, and with small, sparse and yellow leaves and eventually some die-back. Infected roots are black or dark brown, and fine roots are absent. Secondary infection of dead tissues by other fungi is common.
What to do about Phytophthora
Where the disease is new or localized in a garden, affected plants should be destroyed and the soil from the root-run be replaced or treated by a contractor with a chemical soil sterilant. Replanting should be with less susceptible species, which will also benefit from measures to improve soil drainage.
Which plants are most susceptible?
The species most commonly affected by Phytophthora in the British Isles are:
Acer
Aesculus hippocastanum
Calluna
Camellia
Castanea sativa
Chamaecyparis lawsoniana
Erica
Eucalyptus
Fagus sylvatica
Hamamelis
Hebe pinguifolia 'Pagei'
Malus
Nothofagus
Pieris
Prunus
Rhododendron
Rubus idaeus
Syringa
Taxus baccata
Tilia
Current work on Phytophthora at Wisley