Phytophthora Ramorum

Phytophthora ramorum is an oomycete pathogen that causes sudden oak death, a disease that has killed large numbers of oak and other tree species in California and Oregon and has also been found in parts of Europe, producing bleeding cankers on tree trunks and dieback of foliage that frequently kill the tree. Beyond oaks, it infects many other plants, including ornamental species such as rhododendron, viburnum and pieris, in which it causes a milder dieback or blight and which can act as a source of spores that spread the disease further through rain splash and rainwater. First documented in 1995, its origin remains uncertain, though separate introductions into Europe and North America appear likely; control relies mainly on early detection and removal of infected plant material, since treatment options remain limited.