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

FAQ

Frequently Asked Questions

What is sudden oak death or SOD?

What plants are host to Phytophthora ramorum?

What are the symptoms of Phytophthora ramorum?

Who do I contact to learn more about regulations?

Who do I contact if I suspect sudden oak death on or near my home or neighborhood?

Where can I learn more about SOD?

What is sudden oak death or SOD?

Sudden Oak Death (SOD) is a disease of California forest trees and shrubs. Disease symptoms were first reported in 1995 in Marin County and have since been found in wildlands in fourteen additional coastal counties in California, from Monterey to Humboldt, Trinity, and in southern Oregon (Curry County). The pathogen, Phytophthora ramorum (pronounced Fi-TOF-thor-a ruh-MOR-um) is a species of fungus-like microorganism that was identified as the causal agent of SOD in 2000.  The pathogen also causes Ramorum leaf blight that infects over 120 species of California native and horticultural plants other than oaks. Both SOD and Ramorum leaf blight have attracted worldwide concern after it was confirmed 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 prevent the spread of this disease.

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What plants are hosts to Phytophthora ramorum in the North Coast region?

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

 

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 (Notholithocarpus 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 eastern U.S. and European origin

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What are the symptoms of sudden oak death?

The descriptions below are given to provide some summary of the visible symptoms of Phytophthora ramorum and its variability between plants. It is important to remember that these plants are also affected by other pathogens that may cause similar symptoms. Therefore, field identification of this pathogen is not possible and diagnosis requires laboratory confirmation.

 

Overstory trees

 

Oaks and tanoak. In coast live oak, black oak, canyon live oak, and 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 bole. However, bleeding can also be caused by other organisms or by mechanical or natural wounding.  Small charcoal-like fruiting bodies of the fungus Annulohypoxylon thouarsianum (common name: cramp balls) and bark and ambrosia beetles may also be present on SOD-infected trees. Tanoak (not a true oak) is especially susceptible to the pathogen.  Symptoms are very similar to those produced on oaks. Additionally, new shoot growth may droop or discolor creating a "shepherd's crook". Blackened lesions on twigs and sprout stems, as well as blackening along leaf midribs, are also common symptoms.

 

California bay laurel. Symptoms on bay are confined to tree foliage where brown to grey leaf lesions often surrounded by a chlorotic (yellowish) zone manifest mostly on the leaf tip.  These lesions can sometimes can have a blackened line at the border, but not always.  Bay mortality has not been reported although premature leaf drop of infected leaves may have some affect on overall tree growth. Symptoms on California bay are perhaps the easiest to recognize, although anthracnose can also cause similar symptoms.

 

Bigleaf maple. P. ramorum foliar infection on bigleaf maples causes leaf scorching, 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 on California buckeye include brown leaf spots or darkened lesions on the petioles and twigs.  Early symptoms form as rounded individual spots that tend to coalesce later in the growing season. The symptoms are very similar to buckeye anthracnose (refer to the anthracnose link under California bay). Early summer leaf loss in response to drought is normal and not due to Phytophthora ramorum. 

 

Coast redwood. Symptoms on redwood include needle lesions and the cankers on small branches. The pathogen can also cause mortality of basal shoots on mature redwoods.  To date the disease is not known to infect mature tree trunks.

 

Douglas-fir. Symptoms on Douglas-fir 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.  It is hypothesized that the pathogen will only infect Douglas-firs that are surrounded by infected bay trees, but there have been no studies to confirm this.

 

Pacific madrone. Symptoms on madrone include purplish leaf spots and stem cankers that appear as blackened areas on twigs.  At the advanced stages of infection, the entire leaf and shoot blacken and die. All stages of tree development including mature trees are affected.  There are many other pathogens and declines that cause very similar symptoms on madrone making it very difficult to distinguish symptoms of P. ramorum.

 

Understory trees, shrubs, and horticultural plants

(NOTE: 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 also include branch tip dieback.

 

California honeysuckle symptoms are lesions with concentric rings produced on leaves.

 

California rhododendron symptoms include leaf lesions and twig dieback, and in rare instances mortality. Leaf lesions appear as brown spots with diffuse margins  where water accumulates, and generally do not involve the midrib of the leaf.  Additional symptoms are blackened shoots with or without foliage still attached.  

 

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 can 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 canker, a common pathogen that affects many of the same ornamentals as P. ramorum.

 

Toyon symptoms include dark foliar lesions, at times demarcated by a thick black

line where water/moisture accumulates.  Less prominent foliar spots, branch lesion, and atypical 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 spotting or possible twig cankers could be expected symptoms of all of these

species. Bleeding stem cankers occur in poison-oak, horse chestnut, a Mediterranean oak (Quercus sativa), and European beech.

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Who do I contact to learn more about the regulations?

Jeff Dolf

Agricultural Commissioner

Humboldt/Del Norte/Trinity County

5630 South Broadway

Eureka, CA 95503

(707) 441-5260

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Who do I contact if I suspect sudden oak death on or near my home or neighborhood?

Dan Stark stark@ucanr.edu

Sudden Oak Death Outreach Coordinator

OR

Yana Valachovic yvala@ucanr.edu

Forest Advisor and County Director 

 

University of California Cooperative Extension

5630 South Broadway, Eureka CA 95503

(707) 445-7351

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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: www.suddenoakdeath.org

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

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

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Webmaster Email: lacannafax@ucanr.edu