What is Sudden Oak Death ?
Sudden Oak Death is a disease caused by the fungus-like pathogen Phytophthora ramorum. This pathogen has caused widespread dieback of several oak species and non-oak species in the central and northern coastal counties of California. It has been found on several other species, including Douglas fir, rhododendron, California bay laurel, and camellia. While some of these species - coast live oak, black oak, Shreve oak and tanoak - sustain lethal trunk infections, other plants get more benign foliar and twig infections. Many of these species with foliar infections play a key role in spread of P. ramorum by acting as a reservoir of innoculum, which may then be spread aerially via wind blown rain. Sporangia and chlamydospores, the most likely propagules of dispersion, are commonly generated on foliage, whereas they have not as yet been found on infested oak bark. The two plants determined to be the greatest sinks for innoculum are California bay laurel/Oregon myrtle and Rhododendron spp. Mortality is most common where oaks and these foliar hosts are found growing together.
At present, there are 38 species known to be susceptible to the Phytophthora ramorum . 22 of these have been recognized as regulated hosts by the United States Department of Agriculture, Animal and Plant Health Inspection Service - Plant Protection and Quarantine (USDA-APHIS-PPQ), and by the California Department of Food and Agriculture (CDFA). Regulated plants are those adapted from other regulated lists or were added upon completion, documentation and review of traditional Koch's postulates. Some are regulated in part - such as Douglas fir and redwood - while others are regulated in their entirety. These regulated species are now listed in Phytophthora ramorum 7 CFR Part 301.92, and "Recent Modifications to Phytophthora ramorum Regulations" at: www.aphis.usda.gov/ppq/ispm/sod .
An additional 16 plant species are listed as associated with Phytophthora ramorum . Associated plants are those found in nature from which P. ramorum has been cultured or detected using PCR (Polymerase Chain Reaction). For each of these, Traditional Koch's postulates (see below) have not yet been completed or documented and reviewed. Though not regulated and not requiring certification under P. ramorum regulations, these plants will be inspected in nurseries and Christmas tree plantations and, if symptoms are observed, held from sale pending testing.
Summary of Koch's Postulates
