Phytophthora ramorum ( Pr, Sudden Oak Death, Ramorum Blight, Ramorum Die-back ) is a foliar and shoot pathogen currently causing extensive levels of mortality in a variety of oak species of a number of coastal counties in California, from Big Sur National Park north to one county in southern Oregon. Pr is a member of the group of organisms called Oomycetes.

The disease is commonly called Sudden Oak Death (SOD), and although oak are currently the most significantly impacted Pacific Northwest native species, many other plants can be infected by Pr and will suffer various levels of injury, including rhododendron, camellia, viburnum, azalea, big leaf maple, huckleberry, bay laurel and Douglas fir. There are about 70 species currently on the list of hosts.

Much scientific and practical research has been invested by the US government and other agencies in an attempt to understand and contain the spread of Pr., and unfortunately much remains to be learned. There is no currently identified pesticide that will eradicate the pathogen without also destroying the host, therefore containment is the primary countermeasure. Fortunately, the pathogen is easily destroyed through the use of common disinfectants, and nursery sanitation programs are an effective control.

Although Pr can be isolated from infected water, soil and growing media, and lab tests have demonstrated that infection through the root system is possible, it is most commonly believed that the primary point of infection is through the lower surface of leaves and needles in shrubs and through the bark in trees, and most likely where there is a wound or other point of damage. However, the motile zoospore stage of Pr has been demonstrated capable of infecting intact leaf tissue.

The most current belief is that the pathogen is spread in the forest as a result of wind driven turbulent rain conditions in the spring when temperatures and weather conditions are favourable for spore germination. Spread between nurseries is believed to be the result of movement of infected stock. Although movement of Pr outside of the currently infested areas on nursery stock has been confirmed, thorough surveys of susceptible plants around receiving nurseries has failed to find any movement of the pathogen beyond the nursery. It is not currently known from where the pathogen originated.

In most shrubby material, the most common symptom is leaf spotting or needle blight, while in conifers the most common symptom is shoot dieback of the current year's growth, leading to the names Ramorum blight and Ramorum tip dieback, respectively.

Above is a photograph of dieback in Douglas fir from Pr. The symptoms are much like the symptoms of many other disease causing organisms.

The only way to confirm the presence of Pr is through the morphological identification of laboratory cultures and and/or molecular identification at the DNA level.

Inspection and certification

The United States Department of Agriculture (USDA) has enacted legislation to regulate the movement of plant material from the three states of California, Oregon and Washington in an attempt to prevent the possible spread of Pr through nursery stock (native and ornamental) to other parts of the country, particularly to the commercially important red oak forests of south eastern US. In Canada, concern revolves around the potential for damage to the oak savannah ecosystem in eastern Canada as well as to the Garry oak and Arbutus ecosystems of the west coast.

The goal of the USDA is to determine the extent of the pathogen's distribution in the US and to limit the artificial ( human caused ) spread beyond current infested areas through quarantine and public education.

Agriculture Canada's Canadian Food Inspection Agency ( CFIA ) has regulated Pr as a quarantine pest for purposes of import into Canada from the US and overseas for several years.

In response to the concerns of commercial nurseries in the pacific coast states, state governments and the USDA, the British Columbia Landscape and Nursery Association ( BCLNA ) has implemented a voluntary certification program in harmony with the USDA program and under the watch of Agriculture Canada's Canadian Food Inspection Agency ( CFIA ) to participate in preventing the spread of Pr into the US from potentially infected nursery stock in Canada.

Through the independent, non-profit Nursery Certification Institute ( NCI ), British Columbia nurseries who wish to ship stock to the United States, and perhaps ultimately east of British Columbia, will need to be inspected and certified practically free of Pr.

The situation for K&C Silviculture

While infection from both current and new diseases is always a concern, and our participation in the Canadian Nursery Certification Program requires that we use "current best practices" to prevent and control pests and disease, K&C Silviculture's Okanagan Operations is fortunate in being at low risk for Pr.

We do not import juvenile or mature plant material to our site. All of our stock is currently grown from seed, and seed is not believed to be an infectious source of Pr.

Pr prefers cool, wet conditions and temperatures between 10 and 18 C. Current knowledge suggests that periods in excess of 12 hours of favorable conditions in the spring of the year are required for infection, typically associated with foggy coastal weather. The South Okanagan is the northern tip of the Sonoran Desert, and is associated with cold winters, hot summers and low levels of precipitation.

Native areas currently infested with Pr are characterized by heavy growth of highly susceptible species of rhododendron, bay laurel and oak, few of which exist in our area, and only in small ornamental plantings.

All sampling at the Nursery has been verified free of Pr. However, along with others, we are concerned about the potential social, environmental and economic impact of Pr on forests of North America and the associated forest and horticulture industries. We are willing participants in the Pr Certification Program, and we trust it will be of mutual long term benefit to all of us.

Here is a copy of the document received from the British Columbia Landscape and Nursery Association verifying that the samples collected at our facility last fall were tested negative for Pr.

If you are searching for a Certification Permit for our facility from the Canadian Food Inspection Agency verifying that our facility is free of Pr., this is a copy of a letter from the Canadian Food Inspection Agency regarding national certification.

If you have questions or concerns that have not been addressed, please contact the following:

Kent Stralbiski, B.Sc., Biologist
Ph: 250-498-4974 ( Nursery ) or 250-808-0701 ( Cell )
Email: kent@silviculture.com

Further Information

Further information can be obtained from the following organizations:

Agriculture Canada - Canadian Food Inspection Agency

www.inspection.gc.ca/english/plaveg/protect/pestrava/sodmsc/sodmsce.shtml

Canadian Nursery Landscape Association

www.canadanursery.com/canadanursery/index.lasso

United States Department of Agriculture - Animal and Plant Health Inspection Services

www.aphis.usda.gov/ppq/ispm/pramorum/

www.aphis.usda.gov/lpa/issues/sod/sod.html

California Oak Mortality Task Force

www.suddenoakdeath.org