Survey Instruction Details:
Use rhododendron leaves as bait by cutting the leaves in a herringbone pattern. Place 3-4 cut leaves into a mesh bag. Place the mesh bag into the water source for a minimum of 48 hours to 1 week (preferable).
Alder twigs, apple, eucalyptus, and oak leaflets have also been used as baits for P. alni.
A baiting technique using rhododendron leaves has been used in Alaska (Adams, 2007; Adams et al., 2010).
P. alni causes a serious disease of alder (Alnus spp.), including lower stem bark lesions, root and collar necrosis, and crown dieback typical of other Phytophthora diseases.
In mid to late summer, diseased alder exhibit thin crowns and small, pale leaves; the fungus may completely girdle the tree, resulting in death; or narrow strips of bark may remain alive and support limited growth; bleeding cankers on trunks. Leaves frequently fall prematurely, leaving the tree bare. On severely affected trees, tarry or rusty spots are present on the bark at the base of the tree.
Crown decline and the tarry spot symptoms occurring together reliably indicate the presence of a basal stem necrosis produced by Phytophthora spp. After removing the outer bark layers around the tarry spots a red-brown to black discolored necrotic area is exposed. It is mostly tongue-shaped, growing upwards as well as in a periclinal direction.
Although not a specific symptom, the development of adventitious roots can be a useful indication of the presence of a bark lesion further down the stem.
Early and often excessive fructification with unusually small cones is also observed.
General information on detecting Phytophthora spp. is available in O"Brien et al. (2009).