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Phytophthora ramorum

EPPO code

PHYTRA

Common names

English names: Sudden oak death
Nordic names: Californisk/europæisk visneskimmel(DK), Versopolte (FI), Ramorum greinvisning (NO)
Estonian name: Tamme-äkksurm

Major host plants

Phytophthora ramorum has a remarkably wide host range including hardwoods, softwoods, landscape plants and herbaceous plants. To date, more than 75 plant species and cultivars representing more than 45 genera can either be infected by the pathogen or facilitate its spread. In Europe, P. ramorum is mainly found on Rhododendron and Viburnum, but it was also isolated from Arbutus, Camellia, Hamamelis, Kalmia, Leucothoe, Magnolia, Pieris Pseudotsuga, Sambucus, Syringa and Taxus. In the United Kingdom, an isolated finding was reported on one Quercus falcata tree and on a few trees of Fagus sylvatica, Quercus ilex, Q.cerris, Castanea sativa and Aesculus hippocastanum. In summer 2009, the pathogen was detected for the first time on conifer trees (Larix kaempferi). In the Netherlands, infections on one Q. rubra and two Fagus sylvatica have also been reported (all trees were located near infected Rhododendron). In Ireland, P. ramorum has been isolated from one Q. phillyraeoides tree.

Symptoms

P. ramorum produces three disease symptoms:
Shoot dieback: Shoot/stem infections, resulting in wilting and dieback of affected parts.
Leaf blight: Foliar infection, resulting in discoloured lesions on leaves.
Sudden oak death: Lethal cankers with dark, reddish ooze on tree trunks. The cankers gradually expand until they girdle the tree, causing the tree to die. Tree death may occur within several months to several years after initial infection.

In Europe, P. ramorum mainly causes leaf and twig blight.

The Danish AgriFish Agency

See more pictures on EPPO's website

Distribution

P. ramorum is present in North America and the EPPO region.

A map can be downloaded from EPPO's website. See instructions here.

Biology

P. ramorum is a cool temperature pathogen, having an optimum growth temperature of 20°C. It requires moisture to complete its life cycle since wet environments favor spore production, dispersal, germination and infection. Infection occurs through zoospores, sporangia and chlamydospores, which form on leaves of several hosts where splashing water and windblown rain disperse them onto nearby plants. Spores can be found in soil, water, and plant material.

Major pathway(s)

Dispersal takes place locally by rain splash, wind driven rain, irrigation or ground water. Long distance dispersal occurs by movement of contaminated plant material (wood, green material products and nursery stock) or soil from areas where the disease occurs.

Detection and inspection

Before starting the inspection, it is important to be familiar with the susceptible host lists and be aware of the visual symptoms. The probability that the plant is infected with P. ramorum will be greater if it is a known susceptible species, if it exhibits typical symptoms, and if it is located in an infested area. However P. ramorum cannot be identified by visual symptoms alone since many other species of Phytophtora as well as other pathogens can cause similar symptoms. Therefore, laboratory confirmation is necessary for accurate diagnosis. The use of a Phytophthora field test kit provides a fairly good indication of infection.

Pest status and importance

In Europe, the fungus is mostly seen on plant production in nurseries and to a limited extent outside nurseries in plant societies where Rhododendrons are present. The potential impact for Nordic and Baltic areas is expected to only be moderate as long as there are only few foliar hosts with potential for high inoculum production in forests and parks.

Source of information

See further information here:

Author: Jorma Rautapää
Editor: Elise T. Yamamoto Buch

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