Recent research into Phytophthora has revealed another similar pathogen.
Pathogens
Phytophthora ramorum (ramorum blight, popularly known as ‘sudden oak death’) and P. kernoviae.
The former occurs in Europe and in western USA. The latter is a previously unknown species occurring at only a few sites in the UK, mostly in Cornwall, where it was discovered during surveys for P. ramorum. Neither are native to Europe or the USA but their origins are unknown.
Problem
Leaf, stem and bark infections on various native and garden trees and shrubs. Both species are frequent on rhododendrons; viburnums are a major host of P. ramorum only. Bark canker caused by P. ramorum was recently discovered at a single site on Quercus petraea, the first record on a native English oak. Cankers on trees have been relatively rare and most are associated with heavy leaf infection in understorey rhododendrons.
Current status
Both pathogens are notifiable and subject to eradication. Details and illustrations can be found at the websites: www.defra.gov.uk/planth/ph.htm; www.forestry.gov.uk/forestry/infd-5vtlel
Most of the eradication effort is concentrated on nurseries (to prevent spread within and by the trade) and in certain hot spots in established gardens and woodland, particularly in the south-west. Gardeners who detect suspicious symptoms should notify defra’s Plant Health and Seeds Inspectorate (shrubs) or the Forestry Commission (trees).