We always enjoy welcoming new visitors at Bloedel Reserve. But when the grounds crew discovered a small number of diseased plants on the property infected with the pathogen Phytophthora ramorum, we knew immediate action was needed to remove the unwanted guest.
With the help of the U.S. Department of Agriculture (USDA), Washington State Department of Agriculture (WSDA) and Washington State University (WSU), we were able to bring the disease under control.
Earlier this summer, all diseased plants were removed and destroyed in compliance with USDA instructions. The pathogen typically produces spores that allow it to survive and spread in soil and plants. Steaming the soil is an effective, non-chemical way of eradicating the pathogen if the temperature is held at 50C (122 F) for at least 30 minutes and to a depth of six-inches. If you visited Bloedel in late summer, you might have noticed the steamer at work in an effort to eradicate the pathogen from Bloedel. (See photo below)
While it was disheartening to discover the pathogen in the gardens, the quick reaction by our staff, along with the expertise from the government agencies, helped minimize damage. Although we hope such a scenario never happens to another public garden, if it does, we will be a resource for our peers and help them implement best practices in order to minimize the damage.
Ramorum Blight FAQs:
What is Ramorum Blight? Ramorum Blight is also known as Sudden Oak Death (SOD). It is caused by Phytophthora ramorum, a fungus-like organism known as a water mold. There are many Phytophthora species and typically they cause plant disease. Ramorum Blight is particularly virulent with potential for causing significant aesthetic and economic damage in Washington State. In other parts of the world, particularly California, it causes ecological damage as well.
How common is it? Fortunately, Ramorum Blight is not common in Washington State. It’s usually found only in nurseries where it was acquired from out-of-state growers where the disease is more common (like California or parts of Europe). The USDA and WSDA are working with state nurseries to help keep this disease from becoming more widespread.
What are the symptoms of Ramorum Blight? The symptoms can vary depending on the plant host. Foliar symptoms will involve browning of the leaf, especially near the tip where water from rain or irrigation accumulates. These symptoms are caused by other Phytophthora diseases as well, so samples should be sent to the diagnostic laboratory for identification to species.
How damaging is this disease? There is not an easy answer to this question. The severity of the disease depends on the host plant and the environmental conditions. Species like Tanoak and some Live Oaks native to California can be killed relatively quickly (over a few months to a few years). For other plants like Rhododendron and related species, the damage may vary from minor leaf spotting to gradual death. The greatest threat the disease poses in Washington State is to its substantial plant nursery, forest products and Christmas tree industries.
How did you know you had the problem? In March of 2015 we submitted a sample of a diseased Pieris to the WSU Puyallup Plant and Insect Diagnostic Laboratory for diagnosis, not expecting it to be Ramorum Blight. The WSU laboratory determined the sample was infected with Ramorum Blight and alerted the WSDA and USDA as required by law– Ramorum Blight is a federally regulated plant disease. WSDA and USDA labs confirmed that the disease was in fact Ramorum Blight.
How long do you think you had it? We’re not sure. Investigation by the USDA was unable to determine the source.
How do you think the disease arrived at Bloedel Reserve? We don’t know but most likely it was introduced to Bloedel Reserve via purchasing infected nursery stock. We provided the USDA with a list of all nurseries we used to purchase plants over the last two years. The USDA inspected these nurseries but was unable to detect Ramorum Blight.
What plants does Ramorum Blight attack? Ramorum Blight infects a wide range of plant species. The complete list of known plant hosts can be found here. In Washington State, the five most commonly infected species discovered in nursery inspections are Rhododendron, Camellia, Viburnum, Kalmia, and Pieris. Other common plants in our area that can be infected are Salal, Oregon Grape, Bigleaf Maple, and Madrone. These species are often not killed by Ramorum Blight but can serve as a source of infection for more sensitive species.
How is it spread? Ramorum Blight is predominantly spread by water and human transport. Rain and irrigation water can spread the spores to new host plants; people can spread it by planting/replanting/pruning the infected plant. The spores can also hitchhike on clothing, soil, and gardening tools. It’s also possible to spread the disease by planting unknowingly infected nursery plants.
Is it harmful to people and animals? Not to worry! It’s a disease that only affects plants. Ramorum Blight has never displayed the ability to infect any living things besides certain plant species.
Are visitors at risk for bringing the disease home to their gardens? Bloedel Reserve alerted the USDA and WSDA as soon as the disease was suspected and Bloedel worked with the agencies to bring the disease under control. Visitors can help by following rules that have always been in place at Bloedel: stay on the trails, mowed lawns and roads. Visitors should not venture off into the woods or off the trails. Also, as tempting as it can be to take a souvenir, visitors should not take leaves, rocks, pine cones, etc. home as they may inadvertently transport the disease.
How do I know if this disease is in my garden? What should I do if I think my plants are diseased? There is no easy way to tell if Ramorum Blight is in your garden. The disease’s symptoms resemble those of other plant maladies and accurate diagnosis requires submission of a sample to a qualified plant disease laboratory. Washington State University has developed a short set of online questions to help you determine if you need to send in a sample for diagnosis of Ramorum Blight. They also have an online FAQ.
How do you mitigate the disease? Prevention is the best medicine. Specifically, quarantine and sanitation are keys in stopping the spread and introduction of Ramorum Blight. New plants are isolated in quarantine for two months and observed for symptoms of Ramorum Blight. If they remain symptom-free, they are released for planting on the grounds. To deter the spread of the disease tools, footwear, rain gear, etc. are disinfected with alcohol, bleach, or Lysol-related solutions. Plant material and debris from previously infected sites are not used to make compost or mulch. Potentially infected plants are reported to Bloedel’s Plant Health Manager for inspection and testing. Vigilance is key to prevention.
How will you prevent this from happening again? We have worked with the WSDA, USDA, and WSU to develop procedures and practices to prevent the introduction and spread of Ramorum Blight and other plant diseases in general. These include quarantines, proper sanitation, plant selection, exclusion, eradication, and soil steaming.
What else do you monitor for? We continually look for unhealthy plants as a normal part of our plant health care activities. In addition to Ramorum Blight, other potentially significant pests we keep a special eye out for are Brown Marmorated Stink Bug, Asian Longhorned Beetle, and Boxwood Blight.
How does the Bloedel minimize the risk of getting pathogens and pests? Quarantine of new plants is the best way to prevent introducing diseases and pests. All it takes is one infected plant to spread the disease across the grounds!
I need more information! What should I do? Where should I go?