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Forest Research home > Research themes > Protecting trees > Impact of Phytophthora diseases on trees > Phytophthora kernoviae Symptoms of Phytophthora kernoviae
When shoots (buds and young stems) and leaves of rhododendrons are infected they become necrotic and often entire tufts of foliage wilt at the end of the shoots and then desiccate [Photo 1]. By contrast, when the bark of a beech tree is invaded, extensive areas of inner bark often extending 10m or more up the stem are killed and black tarry exudate oozes from the affected areas [Photo 2]. Magnolia leaves, blossom and fruit can also be diseased with the flowers becoming in part or altogether blackened and shrivelled when infected in spring, whereas leaves and fruit become blotched with brown/black necrotic patches [Photo 3].  Photo 1 Shoot tip dieback and leaf wilt of Rhododendron ponticum infected with P. kernoviae, Cornwall, UK, 9 Aug 2005  Photo 2 Bleeding canker caused by P. kernoviae on beech, May 2006  Photo 3 Magnolia tree foliage infected with P. kernoviae, Cornwall, UK, 22 Oct 2004 Over the past two years, a wide range of different magnolia species and hybrids have been found to be suffering from infection by P. kernoviae (see table below). All have been growing in gardens which also had infected rhododendrons, and the rhododendrons have probably acted as the source of infection. However, once the magnolias become infected there is evidence that P. kernoviae can persist on infected tissues over winter and then re-infect the new flowers and leaves that are formed the following spring.
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