Phytophthora ramorum
Detection of "P. ramorum" in watercourses has emerged as the earliest of early detection methods. This technique employs pear or rhododendron baits suspended in the watercourse using ropes, buckets, mesh bags, or other similar devices. If plants in the watershed are infected with "P. ramorum", zoospores of the pathogen (as well as other "Phytophthora" spp.) are likely present in adjacent waterways. Under conducive weather conditions, the zoospores are attracted to the baits and infect them, causing lesions that can be isolated to culture the pathogen or analyzed via PCR assay. This method has detected "P. ramorum" at scales ranging from small, intermittent seasonal drainages to the Garcia, Chetco, and South Fork Eel Rivers in California and Oregon (144, 352, and 689 mi2 drainage areas, respectively). It can detect the existence of infected plants in watersheds before any mortality from the infections becomes evident. Of course, it cannot detect the exact locations of those infected plants: at the first sign of "P. ramorum" propagules in the stream, crews must scour the watershed using all available means to find symptomatic vegetation.
Phytophthora ramorum
"P. ramorum" is heterothallic and has two mating types, A1 and A2, required for sexual reproduction. The European population is predominantly A1 while both mating types A1 and A2 are found in North America. Genetics of the two isolates indicate that they are reproductively isolated. On average, the A1 mating type is more virulent than the A2 mating type, but more variation occurs in the pathogenicity of A2 isolates. It is currently not clear whether this pathogen can reproduce sexually in nature and genetic work has suggested that the lineages of the two mating types might be isolated reproductively or geographically given the evolutionary divergence observed.