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.
Rhododendron album
Pseudomonas cichorii
In 1995, the bacteria "Pseudomonas cichorii" was discovered on container-grown rhododendrons in a nursery in Georgia, USA. The spots were at first very small, one to five millimeters in diameter, but soon grew into large, reddish brown blotches. (Uddin & McCarter, 1996).
Phytophthora ramorum
In 2002 and 2003, studies in nurseries throughout California and Oregon tested for "Phytophthora ramorum". The symptoms of the disease were large necrotic spots with water soaked outside borders and rust colored centers. Symptomatic plants were collected, and DNA was extracted from the spots. After amplifying it with a PCR assay, GenBank matched the DNA to that of "Phytophthora ramorum" and "P. lateralis". In 2004, Rhododendron leaves with similar symptoms were studied and showed the host range of P. hibernalis as well (Blomquist et al. 2005).