Phytophthora ramorum disease

Phytophthora ramorum (P. ramorum) is a fungus-like pathogen of plants that has caused extensive damage and mortality to trees and other plants in areas of the United Kingdom. It has also been found in a number of other European countries as well as the USA where it has caused significant damage and mortality to many trees and plants and where it is often called Sudden Oak Death.

It was first recorded in the UK on viburnum plants in 2002 at a garden nursery site in Sussex but it was not until 2009 that it was found living on Japanese larch trees in the wider countryside in the south west of England. In the following years, it was found throughout the west of England, Wales and Scotland as well as in Ireland. The disease seems to thrive in the wetter, western regions of Britain where the climate is more directly influenced by the Atlantic Ocean and so far very few cases have been confirmed in the drier, eastern areas of the British Isles. In the south west of England, there are large areas that are composed of Japanese larch which is why the disease has had a huge impact on economic forestry in the region.

The disease attacks the tree by killing off branches and creating weeping wounds on the trees called cankers, which will weaken and eventually kill the tree. The disease can also begin to send out millions of spores from an infected tree which can then infect all the surrounding trees. At sites where the amount of spores being released is particularly high, tree species other than larch can be affected, including other conifers as well as broadleaved trees such as sweet chestnut and beech. There is no cure as such – only by felling infected trees can the disease be managed because it requires living tissue to grow, so by felling the infected trees the extent of the disease can be reduced.

The Forestry Commission website contains a wealth of information aboutPhytophthora ramorum disease (as well as other current pest and disease threats to UK trees and forests) including recent updates, an up-to-date map showing locations of the most recent outbreaks and pictures showing the symptoms as they appear on trees.