Sudden Oak Death is the popular name for an emergent and potentially destructive new disease in the United States. The name, Sudden Oak Death (SOD), was initially used to describe the rapid decline of many native tree species first observed by hikers in coastal California forests in the mid 1990s. An unidentified fungus-like organism was isolated from infected trees by forest pathologists in 2000 but the identity of this organism (Phytophthora ramorum) was not confirmed until 2001. To date, natural infections are limited to the West Coast, which includes several coastal counties in California and one county in Oregon. More recently, P. ramorum has also been detected in nurseries in California, Washington, Oregon, and British Columbia. The concern regarding this disease in Connecticut was heightened during 2004 when several shipments of plants from nurseries in California and Oregon were distributed to our state and those from Oregon were later determined to test positive for P. ramorum. As a result of these contaminated shipments, there is justifiable concern that Connecticut forests and landscapes may have been exposed to this pathogen.

Because of our lack of experience in dealing with this newly discovered pathogen, we are unable to make accurate predictions with regard to its spread and potential environmental impact. Many have asked if P. ramorum could be as destructive as the organisms responsible for Chestnut Blight, Dutch Elm Disease, and White Pine Blister Rust. Although we know that these three nonnative, introduced pathogens have a history of destroying chestnuts, elms, and white pines in forests and landscapes, it is just too early to assess the potential of P. ramorum. Quite simply, we don’t know enough about the biology and genetics of this plant pathogen to answer this and many other questions. We need to proceed with caution.

CAUSAL AGENT
Phytophthora ramorum is a fungus-like organism, or oomycete, identified as the causal agent of SOD in 2001. Two races or mating types of the pathogen have been described. Race A1 is commonly found in Europe and Race A2 is predominant in the United States. P. ramorum is not a pathogen of humans or animals. In Connecticut, many other species of Phytophthora are commonly found in landscapes, forests, and production nurseries. Most of these infect roots, are soil- and waterborne, and have limited capability for aerial spread. However, while maintaining the characteristics of its relatives, P. ramorum also appears to have a high capacity for significant aerial dispersal. It is this potential for aerial spread that makes this pathogen particularly destructive. P. ramorum is considered to be a cool climate species with optimal growth at 68ºF but it can grow within the temperature range of 36 to 80ºF. Moisture is also important for survival, spread, and infection of P. ramorum.

HOST RANGE
The plant host range for P. ramorum is broad and extremely diverse. The host list includes herbaceous and woody species, and there are currently 31 "officially proven" or regulated hosts and 37 "officially associated" hosts. Up-to-date lists are available at: http://www.aphis.usda.gov/ppq/ispm/sod/usdasodlist.html. Examples of proven hosts include viburnum, Japanese pieris, several species of oak, Douglas fir, and heather. Greenhouse studies on seedlings of several important East Coast tree species were conducted at the USDA ARS Foreign Disease-Weed Science Laboratory, Frederick, MD. These studies demonstrated the ability of P. ramorum to infect and produce cankers on many of the species tested. Included in this study were chestnut oak, white oak, and northern red oak, species commonly found in Connecticut forests. These findings serve to heighten our concern for East Coast forests.

SYMPTOMS
The disease symptoms associated with P. ramorum are very diverse and primarily determined by the host species. Symptoms can range from oozing, killing cankers on trunks and branches to foliar symptoms. Two distinct sets of symptoms associated with P. ramorum, and the diseases associated with these symptoms, have been called Sudden Oak Death and Ramorum Blight. The disease symptoms characteristic of "Sudden Oak Death" result from lethal stem cankers in the bark, cambium, and outer xylem that expand and girdle the stem and kill the tree. These cankers often ooze and bleed. Tanoaks and certain oaks in the red oak subgenus exhibit these symptoms. Disease symptoms characteristic of "Ramorum Blight" are foliar blighting and shoot dieback. These are the typical symptoms exhibited by many non-oak host species. These symptoms are less severe than cankers and include leaf spots and blotches. In extreme cases, juvenile and mature plants with Ramorum Blight symptoms can be killed.

Unfortunately, disease symptoms characteristic of P. ramorum infections are often indistinguishable from other diseases or effects of insect problems that we frequently encounter in Connecticut woodlands and landscapes. Examples of some look-alike problems are bacterial wetwood, borers, winter injury, mechanical injury, and infections by other fungi. Because of these look-alikes, diagnosis of Sudden Oak Death or Ramorum Blight can be very confusing. If you are in doubt about what is causing a particular symptom on a plant, The Connecticut Agricultural Experiment Station can provide assistance and expert advice.

DISEASE SPREAD
A key avenue for dispersal of P. ramorum over long distances is through shipments of infected nursery stock. Other avenues for spread include infested soils and potting media, and contaminated water. Long-distance spread resulting from shipment of infected nursery stock is precisely the situation Connecticut is facing due to the transport of infected nursery stock from the West Coast. Local spread of P. ramorum commonly occurs from movement of infected plant material, rain and irrigation water, and human activities (e.g., handling plants in nurseries, soil in shoes and tires of hikers and bikers, respectively).

WHAT IS HAPPENING IN CONNECTICUT?
Scientists and state plant inspectors at The Connecticut Agricultural Experiment Station have been watching the situation on the West Coast since the first report of the mysterious, tree-killing disease in 2000. Working with USDA Animal and Plant Health Inspection Service-Plant Protection and Quarantine (APHIS-PPQ), they immediately responded to the needs of Connecticut upon learning of shipments of potentially infected stock to the state. They determined that plants in three of the 56 Connecticut outlets that had received nursery stock from Oregon (in the shipment of plants that occurred from February through September 2004) tested positive for P. ramorum. Since many of the plants in the shipment had been sold as cash-and-carry, it was not possible to account for all of the infected plants. Thus, it is realistic to assume that some infected plants have been placed in the Connecticut landscape.

The detection of P. ramorum in plants shipped to Connecticut raises many concerns and questions, for many of which we have no science-based answers. Will P. ramorum survive and grow in Connecticut? What hosts might contribute to survival and spread in the Connecticut environment? How does it survive adverse conditions? The list goes on. There are many informative websites, fact sheets, publications, and a hotline on this topic. Phytophthora ramorum, the causal agent of SOD and Ramorum Blight, is a serious pathogen with significant potential for economic and ecosystem disruption. It is important to be concerned and aware of this pathogen since early detection is important for containment and management.

The "SOD Hotline" is 1-888-703-4457.

Among the helpful websites are:
California Oak Mortality Task Force: http://www.suddenoakdeath.org/ 
NAPIS: http://ceris.purdue.edu/napis/pests/sod 
USDA APHIS-PPQ: http://www.aphis.usda.gov/ppq/ispm/sod 

The Connecticut Agricultural Experiment Station Contact Information
Dr. Louis A. Magnarelli, Director, 203.974.8440
Dr. Kirby C. Stafford, State Entomologist, 203.974.8485
Dr. Victoria L. Smith, Deputy State Entomologist, 203.974.8474
Dr. Sharon M. Douglas, Plant Pathologist, 203.974.8499

Summary

Sudden Oak Death (SOD) is the popular name for an emergent and potentially destructive new disease in the United States. Phytophthora ramorum is a fungus-like organism, or oomycete, identified as the causal agent of SOD in 2001. Two distinct sets of symptoms associated with P. ramorum, and the diseases associated with these symptoms, have been called Sudden Oak Death and Ramorum Blight. This fact sheet provides an overview of what is presently known about this disease.