UCCE Humboldt - Del Norte Counties
University of California
UCCE Humboldt - Del Norte Counties

Disease Information and Symptoms

Sudden Oak Death (SOD) is a lethal canker-causing disease of forest trees and shrubs. It is caused by a microscopic pathogen, Phytophthora ramorum, that also causes non-lethal leaf blights, stem cankers, and twig dieback in a large number of native and ornamental trees, shrubs, and herbaceous plants in the Pacific Northwest and Europe. In July 2002, the pathogen was found in Redway, the first site in Humboldt County; the county thus joined thirteen other California counties in which the pathogen is established in wild settings. The movement of host materials (leaves, firewood, logs, etc.) within and out of these counties is regulated by State and Federal quarantines to prevent further spread of this disease. Extensive information about the disease, including photographs of susceptible hosts, recent publications and what to do if you think you might know of a host tree or shrub can be found at www.suddenoakdeath.org. For more information on the quarantines contact the Humboldt County Agriculture Commissioner at (707) 441-5260.

 

Frequently Asked Questions:

  • What is Sudden Oak Death?
  • What plants are host to Phytophthora ramorum?
  • What are the symptoms of Phytophthora ramorum?
  • Whom do I contact if I suspect Sudden Oak Death or to learn about the regulations?
  • Where can I learn more?

What is Sudden Oak Death?

Sudden Oak Death (SOD) is a new disease of California forest trees. The disease symptoms were first reported in 1995 in Marin Countyand have since been found in wildlands in thirteen additional coastal counties in California, from Monterey to Humboldt, and in southern Oregon(Curry County). The pathogen, Phytophthora ramorum (pronounced Phy-top-thor-a ra-mor-um) is a newly described species of fungus-like microorganism that was identified as the causal agent of SOD in 2000.  In the brief time since, the pathogen has been found to infect a large number of California native and horticultural plant species besides oak trees. The disease has recently attracted worldwide concern after having been found in wild settings in England and the European mainland. An extensive scientific research team has been formed to study detection, spread, interaction with other host species, possible control measures, biomass removal, etc.  State, national and international quarantines have been established to help to prevent the spread of this disease.

 

What plants can be host to Phytophthora ramorum in our region?

This list is frequently updated.  For the most current and more detailed information visit www.suddenoakdeath.org

 

Overstory trees

bigleaf maple (Acer macrophyllum)
black oak (Quercus kelloggii)
California bay laurel/Oregon myrtle (Umbellularia californica)
California buckeye (Aesculus californica)
canyon live oak (Quercus chrysolepis)
coast live oak (Quercus agrifolia)
coast redwood (Sequoia  sempervirens)
Douglas-fir (Pseudotsuga menziesii)
Grand fir (Abies grandis)
madrone (Arbutus menziesii)
Pacific yew (Taxus brevifolia)
Shreve's oak (Quercus parvula var. Shrevei)
tanoak (Lithocarpus densiflorus)

 

Understory trees and shrubs
California coffeeberry (Rhamnus californica)
California hazelnut (Corylus cornuta)
California rhododendron (Rhododendron macrophyllum)
California honeysuckle (Lonicera hispidula)
cascara (Rhamnus purshiana)
common manzanita (Arctostaphylos manzanita)
evergreen huckleberry (Vaccinium ovatum)
poison-oak (Toxicodendron diversilobum)
salmonberry (Rhubus spectabilis)
toyon (Heteromeles arbutifolia)
wood rose (Rosa gymnocarpa)

 

Horticultural plants and herbs
camellia (various species and varieties)
drooping leucothoe (Leucothoe fontanesiana)
European beech (Fagus sylvatica)
European yew (Taxus baccata)
horsechestnut (Aesculus hippocastanum)
lilac (Syringa vulgaris)
lingonberry (Vaccinium vitis-idaea)
mountain-laurel (Kalmia latifolia)
pieris (various species and varieties)
strawberry tree (Arbutus unedo)
sweet chestnut (Castanea sativa)
viburnum (various species and varieties) 
Victorian box (Pittosporum undulatum)
western starflower (Trientalis latifolia)
witch hazel (Hamamelis virginiana)
various oak species of easternU.S. and European origin

 

What are the symptoms of Sudden Oak Death?

It is important to remember that all of these plants are also affected by other pathogens, the symptoms of which may look similar to those caused by Phytophthora ramorum. Field identification of this pathogen is not possible; diagnosis requires laboratory confirmation. The descriptions below are given to provide some summary of the visible signs of this disease and its variability between plants.

 

Overstory trees

In coast live oak, black oak, and canyon live oak, Shreve's oak, the earliest symptom is the appearance of a bleeding canker often with burgundy-red to tar-black thick sap oozing on the bark surface of the tree bole (and not below the root crown). However, bleeding is a non-specific tree response that can be caused by other organisms or wounding.  Small black conks and bark beetles may also be present with SOD. Tanoak is especially susceptible to the pathogen.  The bleeding symptom is often present though it is less viscous. New growth may droop or discolor. Blackened lesions on twigs and sprout stems, as well as blackening along leaf midribs, are also common symptoms on tanoak.

Click on image to see a guide to symptoms on tanoak and California bay laurel, with hints for collecting them for testing.
Click on image to see a guide to symptoms on tanoak and California bay laurel, with hints for collecting them for testing.

Bay laurel symptoms are confined to brown to grey leaf lesions, often surrounded by a chlorotic (yellowish) zone.  The lesions are most frequent at the leaf tip and generally have a blackened line at the border.  Plant mortality has not been reported. California bay is one of the easier plant species on which to recognize the disease in the field, although anthracnose can also cause similar symptoms.

 

Bigleaf maple, P. ramorum foliar infection causes a leaf scorch, usually starting from the edges of the leaf.  This scorching has irregular borders and does not follow the leaf contour.  Lesions vary in color from orange to brown.  There have been few observations of the disease on bigleaf maple.

 

California buckeye symptoms include brown leaf spots or darkened lesions on the petioles and twigs.  Early symptoms start as rounded individual spots that tend to coalesce later in the season. The symptoms are very similar to buckeye anthracnose. Early summer leaf loss in response to drought is normal and not due to SOD. 

 

Coast redwood symptoms include needle lesions, development of cankers on small branches. The pathogen can also cause mortality of basal shoots on mature redwood trees.  To date the disease is not known to infect adult tree trunks.

 

Douglas-fir symptoms include cankers on small branches of saplings that cause wilting of new shoots, needle loss, and branch die-back, while in smaller saplings, death of the leader and top branch whorls can occur.  The pathogen typically infects only Douglas-firs surrounded by infected bay trees.

 

Pacific madrone symptoms include purplish leaf spots and stem cankers that appear as blackened areas on twigs.  At the advanced stages, the entire leaf and shoot blacken and die. Both juvenile and adult plants are affected.   Botryosphaeria and Natrassia are other pathogens that cause very similar symptoms, making it very difficult to recognize the disease in the field.

 

Understory trees, shrubs and horticultural plants

(The disease is not well understood on many of these plants.)

 

California coffeeberry, lingonberry, mountain-laurel, camellia, and pieris symptoms include dark foliar lesions that vary in size from small leaf spots to large lesions covering half the leaf. Lesion margins are often diffuse rather than precisely defined. Lesions on Camellia and Pieris are located mainly at the edges or tips of leaves, and infected leaves often drop early. Symptoms on Pieris, but not Camellia, often include branch tip dieback.

 

California honeysuckle symptoms include lesions with concentric rings.

 

California rhododendron symptoms include leaf lesions and twig dieback, and in rare instances mortality. Leaf lesions appear as brown spots having diffuse margins (rather than sharp margins as caused by sunburn injury) where water accumulates, and generally do not involve the midrib of the leaf.  Additional symptoms are blackened shoots with or without foliage still attached.  Nursery varieties are also susceptible to this pathogen and many other Phytophthora species in general.

 

Evergreen huckleberry symptoms include twig cankers and cane dieback. The small, blackened twig cankers may be dried and/or wilted. It is common to see patches of dead and live branches. 

 

Lilac symptoms include lesions on leaf edges as well as the death of entire leaf buds. This leaf bud death can appear very similar to twig dieback.

 

Manzanita and strawberry tree symptoms are likely to be similar to madrone with dark branch cankers that can travel quickly throughout the stem and may infect the leaves. The water-soaked appearance of the cankers and the absence of black fungal reproductive structures (pycnidia) may help distinguish the pathogen from Botryosphaeria.

 

Toyon symptoms include dark foliar lesions, at times demarked by a thick black line where water accumulates.  Less prominent foliar spots, branch lesion, and unusual death of entire plants have been reported. 

 

Viburnum symptoms include stem cankers and leaf lesions. Stem cankers often form at the plant base, girdling the plant and causing a wilt that eventually kills the plant. Cankers can also occur on plant branches. Leaf lesions can grow through the leaf and onto petioles or stems to form girdling cankers.

 

California hazelnut, cascara, Eastern U.S.  and European oak species, European beech, European yew, Grand fir, horse chestnut, poison-oak, salmonberry, sweet chestnut, witch hazel, Victorian box: Leaf spot or possible twig cankers could be expected symptoms of these species. Bleeding stem cankers occur in poison-oak, horse chestnut, a Mediterranean oak (Quercus sativa), and European beech.

Whom do I contact if I suspect sudden oak death or to learn more about the regulations?

Humboldt County
Agriculture Commissioner
5630 South Broadway
Eureka CA, 95501
(707) 445-7223 Fax: 445-7220
Del Norte County
Agriculture Commissioner 
2650 Washington Blvd.
Crescent City, CA 95531
(707) 464-7235 Fax: 465-6044

 

Where can I learn more about sudden oak death?

For the most current information about sudden oak death, including photos of the host species symptoms, see the following web sites:

California Oak Mortality Task Force website:www.suddenoakdeath.org

USDA Animal and Plant Health Inspection Service website:
www.aphis.usda.gov/plant_health/plant_pest_info/pram/index

California Department of Food and Agriculture website:
www.cdfa.ca.gov/plant/PE/InteriorExclusion/SuddenOakDeath/index

Or contact:

 

Dan Stark, Sudden Oak Death Program Coordinator, stark@ucanr.edu

Yana Valachovic, Forest Advisor, yvala@ucanr.edu

University of California Cooperative Extension

5630 South Broadway, Eureka CA 95503

Phone:(707) 445-7351

Fax: (707) 444-9334

Webmaster Email: lacannafax@ucanr.edu