Sudden oak death, Phytophthora ramorum

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F o r e s t H e a l t H F a c t s H e e t
Sudden Oak Death Phytophthora ramorum D. Shaw
Figure 1.—Bleeding on bark surface of tanoak. Photos: Alan Kanaskie, Oregon Department of Forestry.
David Shaw, Extension forest health special- ist, Oregon State University.
What is it? Sudden Oak Death (SOD) is a plant disease caused by the water mold Phytophthora ramorum. This organism causes disease in more than 100 species of trees, shrubs, herbs, and ferns.
P. ramorum can infect oak and tanoak directly through the bark, causing an area of dead tissue, a canker, often indicated by bleeding on the bark surface (Figure 1). The tree eventually is compromised and dies. It may look as if the tree dies suddenly, but actually it’s been infected much longer.
P. ramorum causes leaf blight and twig dieback in most host species, especially in rhododen- dron, camellia, and huckleberry. The disease is called ramorum
leaf and shoot blight in these hosts. Common plants in Oregon that are known hosts for P. ramorum, and the diseases in those hosts, are shown in Table 1. For a complete host list, see the Califor- nia Oak Mortality Task Forest website http://nature.berkeley. edu/comtf/
What is at risk? Phytophthora ramorum is an internationally quarantined plant pathogen, and strict restrictions aim to prevent its spread. Quar- antines and regulatory compli- ance impact the economics of growing wood and plants in Ore- gon. We must do all we can to prevent the spread of this disease.
The disease threatens timber trade, the floral-greens indus- try, Christmas tree production, and plant nurseries throughout Oregon. It has the potential to increase fuel loads in forests, thus increasing fire risk. In for- ests, it also could affect slope stability, harm wild mushroom populations, and alter forage and structural components of wildlife habitat. The cost to forests and nurseries in Oregon of eradica- tion and compli- ance work already is more than $10 million.
How is it spread? Sudden Oak Death and the other dis- eases caused by P. ramorum are so
new that information is only now accumulating rapidly. Observa- tions from California, where the disease is widespread, suggest it may be limited to warmer, wetter coastal and near-coastal envi- ronments. In California, disease behavior is linked closely to for- est composition and structure, spreading on California bay laurel (called myrtlewood in Oregon) and killing tanoak. In Oregon, tanoak and rhododendron are the primary hosts on which we know the disease can spread (Fig- ure 2). So far, Oregon myrtle has not become widely infected, as in California (Figure 3, next page).
Local spread of P. ramorum is well documented, but its long- distance dispersal is less well understood. Populations of P. ramorum in California and
Table 1.—P. ramorum hosts and diseases. Disease Host
Sudden Oak Death Tanoak California black oak
Ramorum leaf blight Oregon myrtle Bigleaf maple
Ramorum shoot dieback Evergreen huckleberry Rhododendron Pacific madrone
EC 1607-E • June 2007
Figure 2.—Shoot dieback symptoms of P. ramorum on rhododendron. Photos: Alan Kanaskie, Oregon Department of Forestry.

• Report to OSU Extension for- esters or state or federal for- estry officials if you think you have seen Sudden Oak Death.
• Do not move host materials or soil from the quarantine zone near Brookings, OR.
• When purchasing host plants from nurseries, ask nursery management about the origin of the plants and whether they have been inspected.
For more information Sudden Oak Death and Phytoph-
thora ramorum. A guide for forest managers, Christmas tree growers, and forest-tree nursery operators in Oregon and Washington, EM 8877. 2006. E.M. Goheen, E. Hansen, A. Kanaskie, N. Osterbauer, J. Parke, J. Pscheidt, and G. Chastagner. http://extension.oregonstate. edu/catalog/pdf/em/em8877.pdf
The California Oak Mortality Task Forest http://nature.berkeley.edu/ comtf/
USDA Agricultural and Plant Health Inspection Service (APHIS) http://www.aphis.usda.gov/ plant_health/plant_pest_info/ pram/regulations.shtml
OSU Extension Service http://extension.oregonstate. edu/emergency/oak_death.php
© 2007 Oregon State University. Produced and distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Extension work is a cooperative program of Oregon State University, the U.S. Department of Agriculture, and Oregon counties. Oregon State University Extension Service offers educational programs, activi- ties, and materials without discrimination based on age, color, disability, gender identity or expression, marital status, national origin, race, religion, sex, sexual orienta- tion, or veteran’s status. Oregon State University Extension Service is an Equal Opportunity Employer. Published June 2007
Figure 3.—Symp- toms of P. ramorum on Oregon myrtle- wood (California bay laurel).
Oregon wood- lands belong to a single clone that has repro- duced asexually. This occurs via the prolific pro- duction of spore packets, called sporangia, that can easily break off in rain and
flowing water. Sporangia release spores that can swim through films of water to infect leaves and bark. P. ramorum also can form a resting spore (chlamydospore) that stays in plant material or soil a long time, perhaps more than 1 year, and germinates only under the proper conditions.
People are the best means for long-distance spread of P. ramo- rum, by transporting potted plants or infected wood, leaves, and stems. P. ramorum spores also can survive in soil on bike and vehicle tires and on shoes and tools. If you have been in an infested area in California, remove the soil from these items before you return to Oregon. Do not transport plant material from coastal California to Oregon!
Where did it come from, and where is it now? The origin of P. ramorum is unknown. It also is in Europe, in a population genetically distinct from the one in North America. It appears that both the Euro- pean and North American types of P. ramorum were introduced from an unknown location.
In the urban–woodland interface and in forests, Sudden Oak Death is known only in 14 counties in California and in a 26-square- mile area near Brookings, OR (Figure 4). How SOD came to the Brookings area is not known. No other locations in the wild are known in North America.
Sudden Oak Death has been found in several plant nurseries in Oregon and other states, and these nurseries are under strict inspection and eradication pro- tocols. Each year, new outbreaks are detected, and much effort is spent suppressing the disease.
What is being done? Phytophthora ramorum is being eradicated in Oregon forests (Figure 5) through the coopera- tion of the Oregon Departments of Forestry and Agriculture, the USDA Forest Service, the USDI Bureau of Land Management, and Oregon State University.
Surveys for the disease are done by air and ground and in streams throughout the year. In nurseries, inspections for diseased plants are routine. Whenever infected plants are discovered, they and neighboring plants are destroyed.
What you can do • Do not transport plant mate-
rial or firewood from affected areas in California to Oregon.
• Before returning to Oregon from affected areas in Cali- fornia, wash mud and soil off your vehicle, equipment, clothing, and footwear. If pos- sible, use a 10-percent bleach solution for washing.
• Familiarize yourself with host plants and symptoms of the diseases caused by P. ramorum. This can be tricky! The host list is long, and many other plant pathogens cause diseases with similar symp- toms. See below for some sources that can help.
• Keep on the look- out for infected plants in south coastal Oregon.
Figure 4.—In the wild in Oregon, SOD currently is limited to an area around Brookings (star).
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Figure 5.—Symptoms of P. ramorum infection on a Douglas-fir shoot tip (left) and on grand fir. Photos: (left) Alan Kanaskie, Oregon Department of Forestry; (right) Santa Clara County (CA) Agriculture Department.