SUDDEN OAK DEATH
More than just an Oak Problem
Imagine Tiger Woods plotting his way around Augusta, surrounded not by a blaze of rhododendrons and azaleas but by a few shrivelled brown leaves and dead twigs!
Whilst this will probably never happen, it illustrates the potential threat posed by a plant disease known commonly in the USA as ‘Sudden Oak Death’
JOHN SCRACE, Plant Pathologist, explains more
As we shall see, the organism causing Sudden Oak Death disease can attack more than just oak trees and could, potentially, affect many of the trees and shrubs that provide such an important backdrop to many of our golf courses and parks sports pitches. Let’s start at the beginning. Since 1995, thousands of tanoaks (Lithocarpus densiflorus) and large numbers of other native American oaks (Quercus spp.) have been dying in coastal California and parts of Oregon. The problem was given the name ‘Sudden Oak Death’, and was eventually found to be caused by a microscopic, fungus-like organism called Phytophthora ramorum (from hereon abbreviated to P. ramorum). Phytophthora species have been around for centuries and have a worldwide distribution; they often cause root and stem base rots but, occasionally, affect the aerial parts of plants. For example, potato blight, the disease that caused the Irish potato famine in the nineteenth century, is caused by a species of Phytophthora. P. ramorum does not attack
the roots of the trees, but causes death of the bark
towards the base of the trunk. There is often oozing or ‘bleeding’ of brownish sap from the affected areas of the bark, and this symptom type is commonly known as a bleeding canker. Affected trees lose vigour and, if the bark death girdles the stem, will eventually die.
Depending on the species of tree the leaves may also develop brown, dead patches where they have been infected by the pathogen. Plant health authorities in other parts of the world were soon alerted to the problems caused by P. ramorum in the USA, and began checking for the disease. The potential damage that the disease could cause to oak trees in the UK was taken very seriously, as memories of the devastation caused to English elms by Dutch elm disease were still very fresh. Inspectors from the UK plant health authorities began to check for the disease on nurseries and garden centres, and amenity sites such as parks and gardens. UK inspections began in 2001 and it didn’t take long to find P. ramorum here. In fact, there have now been several hundred
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