Phytophthora ramorum
- cause of Sudden Oak Death in U.S.A and Ramorum dieback in Europe
BACKGROUND
The quarantine organism Phytophthora ramorum has been identified as the cause of Sudden Oak Death
(SOD) in the USA. Since 1995 SOD has been killing large numbers of oak trees along the California coast
of the USA. It has since spread to Oregon. While it is not yet known if European oaks are susceptible, no
symptoms of SOD have been recorded on oak in Europe. In Europe P. ramorum has recently been found to
cause the diseases rhododendron twig blight and dieback, viburnum dieback and Camellia leaf blight.
Other possible hosts have been identified in Europe, including plants of the genera Castanea, Fagus,
Quercus, and Vaccinium. Current scientific information suggests that there are many differences between
the strain of P. ramorum found in Europe and that in the USA (such as pathogenicity, host range and mating
type).
LEGISLATION
The European Community introduced emergency phytosanitary measures to prevent the introduction into
and the spread within the Community of P. ramorum. These measures came into operation on 1st November
2002. The main provisions of the legislation are:
 Member States are obliged to carry out a survey for the organism and report the findings to the
Commission
 Plants of Camellia spp., Rhododendron spp. (other than R. simsii) and Viburnum spp. may not be
moved from their place of production unless they are covered by a plant passport
 Host plants imported from the USA must be accompanied by a phytosanitary certificate and the
plants must either originate in areas in which P. ramorum is known not to occur or alternatively the
plants have been officially inspected and found free of the harmful organism
Action required when Phytophthora ramorum is found in EU
In the event of the organism being found in the EU certain action is now required including destruction of
the infected material and all susceptible plants within 2 metres of the infected plant and retention of all
susceptible plants within a 10 metre radius for at least three months for inspection and testing. All other
susceptible plants on the nursery will be subject to intensive re-inspection following the finding.
SYMPTOMS
The symptoms on rhododendron and viburnum are similar to that caused by other Phytophthora spp. on
these hosts. On Rhododendron spp. the pathogen causes a twig and leaf blight. Affected twigs develop a
brown to black discolouration that spreads along the twig and can spread into the leaves via leaf petioles.
Characteristic symptoms include blackening of the petiole (leaf stalk), leaf base and leaf tip and may extend
along the mid-rib. Leaf infection can also occur without twig infection. In contrast, Viburnum spp. do not
show twig blight and infection usually begins at the stem base and spreads upward, causing the plants to
wilt and collapse very quickly. Brown to black leaf infections, especially on evergreen species, may also be
observed and the pathogen can also affect flowers. On Camellia spp. the pathogen usually only causes leaf
infections. Leaf lesions are usually brown to black, typically occurring at the tip or edges of the leaves.
HOST PLANTS
Adiantum aleuticum, Adiantum jordanii, Acer macrophyllum, Acer pseudoplatanus, Aesculus californica,
Aesculus hippocastanum, Arbutus menziesii, Arbutus unedo, Arctostaphylos spp., Calluna vulgaris,
Camellia spp., Castanea sativa, Fagus sylvatica, Frangula californica, Frangula purshiana, Fraxinus
excelsior, Griselinia littoralis, Hamamelis virginiana, Heteromeles arbutifolia, Kalmia latifolia, Laurus
nobilis, Leucothoe spp., Lithocarpus densiflorus, Lonicera hispidula, Magnolia spp., Michelia doltsopa,
Nothofagus oblique, Osmanthus heterophyllus, Parrotia persica, Photinia x fraseri, Pieris spp.,
Pseudotsuga menziesii, Quercus spp., Rhododendron spp. (except R. simsii), Rosa gymnocarpa, Salix
caprea, Sequoia sempervirens, Syringa vulgaris, Taxus spp., Trientalis latifolia, Umbellularia californica,
Vaccinium ovatum, Viburnum spp.
ACTION IN THE EVENT OF SUSPICION
Please contact the Horticulture and Plant Health Division of the Department of Agriculture, Fisheries and
Food, phone (01-5053585) immediately if suspicious symptoms are observed. Isolate the suspicious
plant(s) and refrain from moving host plants from the nursery.
Figs. 1 and 2. Symptoms of Phytophthora ramorum on Rhododendron spp.
Fig. 3. Symptoms of P. ramorum on Viburnum spp. and Fig. 4 on Camellia spp.
Further information can be viewed on the website of the European and Mediterranean Plant Protection
Organization (EPPO – www.eppo.org) by clicking on the following links:
Phytophthora ramorum
Phytophthora kernoviae