History
Risks to Forests
Symptoms and Identification
   On Oak & Tanoak
   On Other Hosts
How P. ramorum is spread
Regulated Hosts

Introduction (continued)

Symptoms and Identification on Other Hosts

In contrast to the disease symptoms on oak and tanoak, on woody ornamentals we typically observe a range of foliar symptoms including shoot blight, shoot necrosis, and leaf spots or leaf blight. Roots may be infected but look healthy.

Many nursery plants are hosts for Phytophthora ramorum. The ornamentals most affected are, in order of importance, Camellia, Rhododendron, and Viburnum. Other important nursery hosts are Pieris, Kalmia, Magnolia, Leucothoe, Osmanthus, and Syringa.

On Camellia, infected leaves may fall off the plant but  they continue to show typical symptoms of Phytophthora infection: namely, dark brown lesions with defined margins.

On Viburnum and other nursery hosts, Phytophthora ramorum causes shoot dieback and leaf blight. For photos of other nursery plants infected with Phytophthora ramorum see Links.

Symptoms on conifers include needle blight and tip dieback. These symptoms occasionally appear on young Douglas-fir, grand fir, and coast redwood trees growing in forests infested with Phytophthora ramorum.

Diseases caused by Phytophthora ramorum are impossible to distinguish from other Phytophthora diseases by simply examining affected plants in the field. That is why plants with suspected Phytophthora infections must be sent to a lab to confirm a diagnosis of Phytophthora ramorum.

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