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Sudden oak death
Phytophthora ramorum
Synonyms
 
  • ramorum leaf blight
  • ramorum dieback

Plant hosts
 
P. ramorum naturally infects more than 100 different plant species. The USDA APHIS PPQ maintains a complete list of plants on which P. ramorum has been detected.

Symptoms
 
On tanoaks, certain oak species, and beeches, sudden oak death is characterized by bleeding cankers that girdle the trunks of the trees, leading to tree death. Death of the tree often appears to happen very quickly, although the tree may actually have been infected for several months. On other hosts such as rhododendron, pieris, and viburnum, the pathogen causes leaf blight and shoot dieback. If left unchecked, the dieback on some highly susceptible cultivars and species may become severe enough to kill the plant. P. ramorum symptoms on rhododendron are virtually identical to those caused by other aerial Phytophthora species. On still other hosts such as California bay laurel, these leaf spots almost always start on the leaf tip.
 
Symptomatic bay laurel leaves Stem canker on a tanoak
Symptomatic bay laurel leaves             Stem canker on a tanoak
 
Pieris dieback    Symptomatic viburnum
Pieris dieback                                     Symptomatic viburnum


Transmission
 
The pathogen forms deciduous sporangia (spore sacs) in response to moisture. These spore sacs then spread naturally in infested forests through rain and wind events. P. ramorum also forms chlamydospores (long-lived, environmentally resistant spores); these have been detected in soil, including mud collected from hiker's boots, and in plant debris. The pathogen has been recovered from baits placed in streams flowing through natural areas infested with the disease. P. ramorum can also spread through the movement of infected plant material, including nursery stock.

Geographic distribution
 
Canada (in nurseries in British Columbia)
 
United States: California (Alameda, Contra Costa, Humboldt, Lake, Merin, Mendocino, Monterey, Napa, San Francisco, San Mateo, Santa Clara, Santa Cruz, Solano, and Sonoma counties) and Oregon (162 sq. mi. area in Curry County) in natural areas. In 2008, it has also been detected in nursery stock in the following states: California, Florida, Georgia, Mississippi, North Carolina, Oregon, South Carolina, Texas, and Washington.
 
Europe: Belgium, Denmark, Finland, France, Germany, Ireland, Italy, Lithuania, Netherlands, Norway, Poland, Slovenia, Spain, Switzerland, Sweden, and United Kingdom.

Applicable regulations
 
The USDA Animal and Plant Health Inspection Servics (APHIS) has adopted federal regulations requiring the inspection and certification of West Coast nursery stock as free of P. ramorum. In addition, Oregon has adopted regulations for the quarantine area in Curry County and for nursery stock grown within the state.
 
Return to plant pathogen list.