Bleeding Canker on Oak trunk
findings covering most of the UK, and the disease has also been found in many countries of mainland Europe including France, Germany and the Netherlands. The situation with P. ramorum in the UK and the rest of Europe has so far been rather different to that in the USA. The vast majority of findings have been on nurseries and, rather than oak trees, the most common host plants have been ornamental shrubs, particularly Rhododendron and Viburnum species. The disease has been found on a large number of other shrubs, including camellia, Pieris, Kalmia, Hamamelis, and Leucothoe.
The symptoms caused by P. ramorum on shrubs vary according to the plant species, but again it is the above ground parts of the plant that are attacked. On rhododendron the most common symptom is a brown lesion spreading down the middle of the leaf, with the disease eventually working its way down the leaf stalk and into the branch or stem to affect the bark. If the bark is girdled, then death of
branches or even the whole plant may occur. On viburnum, the infection is most commonly seen at the base of the stem - once again if the lesion girdles the stem then wilting and death of the plant follows.
Because the disease was being found on such a range of plants in Europe, the common name of ‘Sudden Oak Death’ seemed somewhat inappropriate. It was therefore given the names ‘ramorum dieback’ or ‘ramorum leaf blight’, depending on the symptoms caused. P. ramorum has the status of a ‘Notifiable Disease’ meaning that all suspect cases must be reported to the relevant plant health authority, who will take statutory action to try and eradicate it.
In addition to the nursery findings, cases of the disease have also been found quite frequently on amenity sites, particularly in the west and southwest where the higher annual rainfall is favourable for the pathogen. The vast majority of these cases have involved the wild rhododendron, Rhododendron ponticum, the purple flowers of which are such a common sight in late spring and early summer. If the disease were confined to this plant there would be no great loss. Whilst its flowers may look pretty for a few weeks, wild rhododendron is a thug, threatening woodland ecosystems by preventing any other plants from growing beneath it.
So what of the threat to UK 12th green at Augusta
oaks from P. ramorum? The Forestry Commission is still undertaking research, but it appears that our native oak species (sessile and pedunculate oak) are much more resistant to the disease
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