Introduced Pests Outreach Project

Sudden Oak Death (Ramorum Blight)

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Scientific Name (of causal agent): Phytophthora ramorum
Common Name (of disease): Sudden Oak Death, ramorum blight, ramorum die-back

Known Hosts:

Bark Canker hosts (infection in trunks):
On the West Coast, species that have been infected include: coast live oak (Quercus agrifolia), black oak (Quercus kelloggii), Shreve oak (Quercus parvula), tanoak (Lithocarpus densiflorus).
At least two eastern oak species, pin oak (Quercus palustris) and northern red oak (Quercus rubra) are susceptible to the disease, when inoculated with the pathogen in the laboratory.

Foliar hosts (infection in leaves and small branches):
Rhododendron (including azalea)-[all species, hybrids, and cultivars], Viburnum spp., Camellia spp., Pieris spp., huckleberry (Vaccinium ovatum), bay laurel (Umbellularia californica), madrone (Arbutus menziesii), California buckeye (Aesculus californica), tanoak (Lithocarpus densiflorus)
Rhododendron and Kalmia native to the eastern region are very susceptible in lab testing.

For the APHIS List of Plants Regulated and Associated with Phytophthora ramorum see:

For a review of the natural hosts of P.ramorum and lab susceptibility tests completed see:
Hosts of Phytophthora ramorum with notes on geographical distribution and mating types) from the Canadian Food Inspection Agency

Symptoms on bark canker hosts:
Black or reddish ooze bleeding from cankers (Figure 1)
Under the bark, black zone lines surround necrotic tissue (Figure 2)
Crown dieback and tree mortality. Trees may retain the brown leaves for months. (Figure 3)

Symptoms on Rhododendron (foliar host):
Leaf spots with a diffuse margin. (Sunburned leaves have a sharper margin.) (Figure 4)
Twigs have a brown to black cankers. (Figure 5).

Symptoms on Viburnum (foliar host):
Infection begins at the bases of the stem. Stem shows discoloration. (Figure 6)
Wilting of the entire plant. (Figure 7)
Leaf lesions and shoot dieback. (Figure 8)

Symptoms on Pieris and Camellia (foliar host):
Camellia- Leaf lesions at leaf tip or margin with diffuse margins. (Figure 9)
Pieris- Necrotic leaf spots and shoot dieback (Figure 10)

Similar disease symptoms or insect damage:
Oak wilt, Oak decline, red oak borer damage
USDA Pest Alert describes Eastern Oak disorders

Many Phytophthora spp. cause similar symptoms. Laboratory analysis is needed to differentiate between Phytophthora species.
Foliar damage caused by P.ramorum looks similar to damage caused by abiotic factors such as cold, drought, sun scald, and chemical injury. The margins of lesions caused by Phytophthora are fuzzy while the margins of the lesions on sunburned leaves are distinct.

Fact sheets and references:
USDA/APHIS Sudden Oak Death Website
contains regulatory information, hosts lists, and current updates on the SOD situation in the U.S.

USDA Forest Service Sudden Oak Death Website
Forest Service Fact Sheets and links to other sources

California Oak Mortality Task Force
Many excellent resources on SOD including full color nursery diagnostic guides

USDA, APHIS publication showing symptoms on foliar hosts

Parke, J.L.; Rizzo, D.M. 2011. Phytophthora ramorum. United States Forest Service.

last reviewed December 30, 2014

Massachusetts Department of Agricultural Resources
Massachusetts Introduced Pests Outreach Project is a collaboration between the Massachusetts Dept. of Agricultural Resources and the UMass Extension Agriculture and Landscape Program. This website was made possible, in part, by a Cooperative Agreement from the United States Department of Agriculture's Animal and Plant Health Inspection Service (APHIS). It may not necessarily express APHIS' views.