Module 2: Disease Management
Module 1: Biology, symptoms, and Diagnosis
Welcome Module 3: Phytophthora ramorum Conclusion Take the Exam Further Information

Disease Cycle



Practice Questions








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.

Tipblight on rhododendron.
Shoot blight on Rhododendron.

Photo by E. Hansen.
Leaf blight on rhododendron.
Leaf blight on Rhododendron.

Photo by J. Hedberg.
Shoot dieback and leaf blight on rhododendron. Shoot dieback and leaf blight on rhododendron. Shoot dieback and leaf blight on rhododendron.
Shoot dieback and leaf blight on rhododendron.

Photo by E. Hansen.


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.

Camellia typically loses its leaves when infected with Phytophthora. Symptomatic leaves are generally visible under the plant canopy for a few days after they have dropped.

Photo by N. Grunwald.

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.

Viburnum x bodnantense ‘Dawn' showing tip dieback and necrosis.
Viburnum x bodnantense ‘Dawn' showing shoot dieback and necrosis.

Photo by Oregon Department of Agriculture
Viburnum plicatum tomentosum ‘Mariesii' showing leaf blight.

Photo by Oregon Department of Agriculture

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.

Tip blight on grand fir.
Tip blight on grand fir.

Photo by Santa Clara Agriculture Dept.
Tip blight on Douglas fir
Tip blight on Douglas-fir.

Photo by D. Rizzo.

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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