I think this page should be eliminated (SMD)–information about Ramorum Blight (SOD) has been incorporated into the new page “Tree Diseases-Exotic and Native.”
This page seeks to answer some of the basic questions Connecticut’s arborists and tree professionals may have about Sudden Oak Death, also known as ramorum blight. For more detailed information, interested individuals are encouraged to explore additional web resources and to keep in touch with information coming out of the Connecticut Agricultural Experiment Station, the Animal and Plant Health Inspection Service and the CT Department of Environmental Protection Division of Forestry.
A note on terminology: The preference among professionals is now to call the complex range of damage to plants caused by the organism Phytophthora ramorum ‘ramorum blight’ rather than Sudden Oak Death, for a variety of reasons. The most important is that ramorum blight is more inclusive of the range of host species that this organism affects, and of the type of damage it causes. Sudden Oak Death focuses attention on the bark lesions and cankers the disease organism causes on oak trees; ramorum blight includes those symptoms as well as the browning, water-soaked appearance that is apt to characterize this disease on such plants as rhododendrons and camellias.
On this web page, both terms will be used, often somewhat interchangeably. However, Sudden Oak Death (SOD) is used much more extensively, due to the date when the page was first written. The reader should be aware that both terms are in use, that they both refer to damage due to Phytophthora ramorum, and that there is a growing preference for referring to the disease as ramorum blight rather than Sudden Oak Death.
What is Sudden Oak Death? TOP
Sudden Oak Death (SOD), also known as ramorum blight, is a plant disease caused by an organism that has the scientific name Phytophthora ramorum. ‘Phytophthora’, of course, is the genus name, like ‘Quercus’ is in white oak, while ‘ramorum’ is the species name again, like ‘alba’, in ‘Quercus alba’, white oak.
Bleeding canker on California white oak (photo courtesy of CA Oak Mortality Task Force)
There are already several kinds of Phytophthoras present in Connecticut, known mainly by the diseases they cause. This list includes Phytophthora infestans, which causes late blight of potatoes and tomatoes, P. cinnamomi, which causes root rot and wilt in azaleas and rhododendrons as well as other diseases, P. inflata, which causes pit cankers in elms and P. cactorum, which causes crown cankers in dogwoods and bleeding cankers in many tree hosts. Phytophthoras are not new to Connecticut, but Phytophthora ramorum is.
Phytophthoras fall into a general class of fungi known as oomycetes, or water molds. As the name implies, moisture is important to these organisms. Phytophthora‘s generally rely on soil, already diseased plants, dead tissue from infected plants, or splashing or running water for their spread. Most (but not all) Phytophthora species have several host species, and cause a variety of symptoms that depend upon the individual host species. As described in the Diseases of Trees and Shrubs (Sinclair, Lyon and Johnson), damage caused by Phytophthoras include blight, dieback, fruit rot, cankers, collar rot, root rot and necrosis of feeder roots (page 284). Incidentally, the word phytophthora comes from the Greek for plant destroyer. (Please see Diseases of Trees and Shrubs for a more complete description).
Sudden Oak Death (SOD) was unknown in the United States before 1995. The term was originally used to describe the sudden death of large numbers of tanoaks (Lithocarpus densiflora) in parts of northern and central California. It was not until the year 2000, however, that the causal organism for this new and frightening problem was identified. Since then, some 28 plants have been identified as hosts of the disease organism, while more than 30 other plants have been identified as being associated with SOD. This second list includes several tree and shrub species common in the northeast. This has raised great concern for its possible spread here. (Red oak, European beech, horsechestnut and mountain laurel are all on this associated list click here to see the full APHIS list.
How serious of a disease is it? TOP
For the northeastern United States, that is an open question. Studies on eastern plant species have generally been laboratory studies therefore, it is unknown whether the organism is capable of becoming a major factor in the natural environment. Climate, including temperature and rainfall, the range of species available to the disease, competition from other organisms and other variables may or may not favor the establishment of P. ramorum in our environment.
As for the harm that the disease has caused in California, it is extensive, particularly with regards to the native oaks of that state. Estimates put the number of oaks and tanoaks killed by SOD in the tens of thousands. In California, the most obvious symptom on the oaks are bleeding cankers found on the trunks of infected trees and their sudden death shortly after the disease becomes apparent.The SOD organism also infects other plants. While this organism does do harm many of these species (e.g., rhododendrons and bay laurel), the damage tends to be less severe, usually occurring in the form of leaf or twig problems. Often, these plants are not killed. Oaks, however, continue to succumb to the SOD disease throughout the woodlands in north and central California.
Tanoak killed in the Big Sur region of California (photo courtesy of CA Oak Mortality Task Force)
I have heard that SOD has been found in Connecticut. Does this mean we now have it here?
Rhododendron leaf showing symptoms of SOD. (photo courtesy of CA Oak Mortality Task Force)
Again, that is something of an open question. The organism that causes Sudden Oak Death has been found on container ornamental plants that were shipped to garden centers and retail outlets in Connecticut. Not all of the plants from these shipments have been found, and and it is highly likely some of the P. ramorum infected plants have been planted in landscapes throughout the state. Since these shipments occurred in the months from February to September 2004, it is reasonable to say that there is a high probability that P. ramorum has been in Connecticut, in an uncontrolled manner, for several months now.
But this does not automatically mean that the SOD organism has spread from these infected nursery plants to plants in the wild. Nor does it mean that the organism will be able to survive in the state or that it is capable of doing the same level of damage to Connecticut s trees that it has caused in California. Since the term “Sudden Oak Death” really refers to the impact of the disease organism on the plants, especially the oak trees, there is a distinction between the occurrence of SOD and the presence of P. ramorum in the state.
On whether we have Sudden Oak Death, or even a population of P. ramorum that is viable in Connecticut, the jury is still out. However, it is important for all plant health professionals to be aware this disease and of the organism, and be prepared to deal with it if they happen to come across signs or symptoms pointing to either.
What should we be doing about SOD?
As a tree health care professional, perhaps the most important thing to do is to familiarize yourself with the disease, its symptoms and its range of host plants. There are many good resources available for you to use, including several on the internet. A good first stop is the home page of the California Oak Mortality Task Force (nature.berkeley.edu/comtf). Among the materials that they have produced is a very useful 13-page summary of the disease, its symptoms and range of hosts. This publication can be downloaded through the following link: Diagnosis and Monitoring of Sudden Oak Death.
The USDA Forest Service has produced a Pest Alert on SOD written specifically for people in the eastern half of the country. This publication can be found at: http://www.na.fs.fed.us/spfo/pubs/pest_al/sodeast/sodeast.htm. Finally, the federal governments Animal and Plant Health Inspection Service (APHIS) also has a toll-free hotline – 1-888-703-4457.
After you have familiarized yourself with the symptoms, it is important to be very observant regarding the occurrence of these symptoms on potential host plants. This will not be easy, as many of the symptoms, especially the foliar and twig symptoms, do not appear greatly different from the general range of leaf spots, drought stress symptoms, frost damage and other common blemishes found on many landscape plants. Nonetheless, careful observation by knowledgeable professionals is the most likely way for this disease to be found early enough so that effective action can be taken to limit its spread in the northeast.
SOD on red oak (Photo courtesy of CA Oak Mortality Task Force)
SOD on mountain laurel (Photo courtesy of CA Oak Mortality Task Force)
What should I do if I think I have found SOD? TOP
Call the Connecticut Agricultural Experiment Station immediately! Feel free to use any of the following phone numbers:
Plants and Plant Diseases:
Dr. Sharon Douglas:
Dr. Victoria Smith:
Dr. Kirby Stafford:
Dr. Lou Magnarelli:
Tell whomever you speak to at the Experiment Station exactly what it is you have seen, on what type of plant and where that plant is located. Do not take samples in from the field that only increases the potential for spread. Allow inspectors from the Agricultural Experiment Station to come out to the site and make their judgment. They will respond quickly, and they will be able to tell you exactly what you should do once they have made a determination about the specific situation.
At the same time, it is probably best not to talk too openly of what you think you may have found until you have spoken with the Experiment Station. In other words, dont call the press! The folks at the Experiment Station and APHIS will need a lot of public cooperation if this disease is to be managed in Connecticut. They do not want to lose the opportunity for cooperation through premature stories and unverified reports of the disease. Your help in this regards is greatly appreciated.
Finally, be vigilant but be patient. Even if Sudden Oak Death turns out to be a virulent disease in Connecticut, its effects may not be noticed for several years. After all, even a relatively fast moving disease like chestnut blight took nearly twenty years to blanket the state. The incubation period for SOD might turn out to be several years, so symptoms might not show on trees like the oaks until a few growing seasons have passed by.