New data on sudden oak death
During the last few months, new and important information on sudden oak death (EPPO Alert List) has been made available through Internet:
- Distribution in California
In addition to Marin, Monterey, Napa, San Mateo, Santa Cruz and Sonoma counties, the presence of sudden oak death is now also confirmed in Santa Clara and Mendocino counties (as of July 24th 2001).
- Host plants
In California, the pathogen (Phytophthora sp.) has been isolated from new host plants:
- Quercus parvula var. shrevei (Shreve’s oak). Symptoms are the same than those on coast live oak (Q. agrifolia).
- Vaccinium ovatum (huckleberry). Affected plants show twig dieback and in advanced stages, they are killed. This finding raises the question of the susceptibility of cultivated Vaccinium, which is unknown, so far.
-;Aesculus californica (buckeye, Californian native tree species), Arbutus menziesii (Madrone) and Umbellularia californica (Bay laurel). The pathogen was recovered from these plant species, but it has not been demonstrated that it could kill them. However, they could play a role in the epidemiology of the disease.
- A similar pathogen has been found in Europe
A similar Phytophthora sp. has been found on rhododendron in the Netherlands and Germany, and was once detected on Viburnum in Germany (symptoms on these hosts can be viewed on DEFRA web site, UK and from BBA web site, DE). It may be recalled that in California, the American pathogen has been found in rhododendron plants adjacent to infested oaks. Further studies are being done to clarify the relationships between the two forms of Phytophthora involved. It must be stressed that no symptom of any such disease on oaks has ever been seen in Europe.
A publication is in press in Mycological Research describing the European pathogen as Phytophthora ramorum. The NAPPO Pest Alert considers that this same species causes sudden oak death in California.
BBA, DE – An unknown Phytophthora species on Rhododendron and Viburnum by Dr S. Werres.
DEFRA, UK – Sudden oak death, rhododendron shoot canker and viburnum dieback.
NAPPO Alert List – Phytophthora ramorum
University of California, Berkeley
Press Release of 2001-10-01.
UC researchers announce results that could complicate measures to halt spread of Sudden Oak Death by C. Zandonella.
Monthly reports of the California oak mortality task force.