SOD Discussion Sessions

• Sudden Oak Death: Focusing Research and Development Activities
• Managing epidemics and worldwide spread of Sudden Oak Death
• Open Topics

This session was intended to provide an open forum for comments, discussion, and suggestions on research and development activities needed to further our understanding of Sudden Oak Death. As moderator, I asked particularly for discussion on high priority information needs that should be addressed as soon as possible. For example, were there particular "data gaps" that if filled would help increase our understanding of Phytophthora ramorum (P.r) and the disease(s) it causes?

The desire was to have a scientific forum with open and lively discussion that focused on information needs as researchable topics and the desired development products for managers dealing with the disease. As background for this discussion, the following areas of potential research interest and need were provided:

BIOLOGY, EPIDEMIOLOGY, AND BEHAVIOR

• Conifers vs. hardwoods (alleochemistry) and susceptibility to P.r
• Variations among hardwood and conifer susceptibility to P. r
• Host chemistry
• Resistance
• Response to infection - host physiology
• Environmental conditions
• How do trees die?

• What is the problem with positive PCR detection and the inability to culture this organism?
• Develop reliable culture techniques for chlamydospores
• Design new, rapid, and simple field testing tools to assess presence of P.r.
• Model theoretical spread of P.r. to other states - "Risk of various pathways"
• Means and mechanisms of long distance dispersal
• Effects of environmental conditions, including temperature, pH, etc.
• Levels of associated microbial antagonism and role in infection process

• Determine "safety margins" in handling conditions during composting
• Test the efficacy of cleaning procedures on equipment used in logging, arboriculture, and recreation
• Test the probability of re-infection of "clean" compost material
• Continue efficacy testing of new chemical treatments
• Develop and apply current knowledge of P.r. to risk models to other areas (entire U.S., Europe, New Zealand, Australia, and Mexico)
• Levels of associated microbial antagonism and role of infection process
• Is there resistance in bay and tanoak?
• Effects of changing composition and conditions of composting units to assess efficacy
• Test adding "natural toxicants" to composting procedures

• Evaluate SOD impact on mychorrizae community, especially as a result of losing understory
• Develop fire risk models - characterize fuel moisture/amount, evaluate for different climatic zones, vegetation types, etc.
• Does SOD increase fire risk?

• Describe regional, national, and international economic and social impacts of Sudden Oak Death
• Quantify the cost of quarantine on nursery stock, agricultural products, and forest "added-value" products

• Determine whether potting media and/or components will harbor P.r. propagules
• Are reproductive propagules of P.r. found in redwood sawdust, sand, and other potting soil components, and are they viable?
• What types of propagules are found?
• How long do they remain viable?
• Can these potting soil components support the growth and reproduction of the pathogen if introduced into the finished potting media?
• Determine whether P.r. can successfully move from the soil in a potted plant to infect and cause disease in another plant, thereby demonstrating spread of the pathogen
• What level of inoculum is needed to cause a new infection?
• What is the threshold level?
• How well do detached leaf inoculation assays correlate with the risk of a natural infection?
• Determine the efficacy of additional fungicides for treating nursery stock, particularly fungistatic treatments: do they mask symptoms?

• What is the risk to Native Americans of ingesting infected host plants?
• What is the likelihood of spread of SOD by cultural use of host plants?
• What non-chemical treatments (heat treatment, etc) can be developed to treat culturally important host plants? What are the health risks of various fungicides that might be used to treat SOD infected plants that are culturally important?

Unfortunately, the bulk of the discussion in the session did not focus on these issues but rather on why scientists working on this disease were not investigating acid rain and ozone as drivers of the damage. Repeated attempts to clarify with appropriate data why these phenomena were not likely major contributors to the Sudden Oak Death situation failed to refocus the discussion on high priority information needs.

The above-mentioned topics are still viewed as priorities for assessment and action. Scientists and other interested parties are urged to continue addressing these needs.

Managing epidemics and worldwide spread of Sudden Oak Death - Session II
Jennifer Juzwik, moderator

Papers in two symposium sessions (IV. Can Sudden Oak Death Be Controlled? - Perspectives from Ornamental Crop Pathologists, and VI. How Can We Slow the Spread of the Disease and Prevent New Introductions?) served as the springboard for discussion on this session's topic. Additional information and perspectives were offered by numerous online participants. The following briefly summarizes the lively discussion resulting from these inputs.

Managing epidemics
One discussion thread addressed the appropriateness of the term "epidemic" for the SOD situation. One participant concluded that the term "epiphytotic" is more appropriate but that the common usage of "epidemic" has prevailed. The core of the discussion on this subtopic focused on practical management of SOD and observations on SOD management strategies. Lively debate arose from discussion of actual "triggers" or "real causes" of SOD (not covered here). The potential for nutritional management (including use of calcium to ameliorate acidic soil conditions) was discussed at length by several participants. In addition, the potential of fungicides to manage the disease through treatment of individual plants was discussed. Both nutritional management and fungicidal management, however, are not likely tools for abating established epidemics of SOD at the forest landscape scale. Several points were raised in discussing an overall strategy for managing SOD. Participants appeared to agree that a multifaceted management approach is needed. For example, one cannot rely solely on chemical treatment or place reliance on the mere presence of genetic variability of various host populations in the forest. However, there is a need to continue to pursue resistance research through screening and breeding work. Broad research on the pathogen, P. ramorum, and SOD (including the biological and epidemiological aspects) should be continued so that a range of management tools and options will be available for forest managers. Finally, approaches should consider the role of predisposition (e.g., acidic soil condition) in the development of SOD in California forests. A few specific comments were made by discussion participants on practical management options. SOD in treed residential lots and gardens may be manageable with chemical controls. In the forest, the aerial application of phosphite for controlling the disease could be considered. The chemical has been used in Australia to combat the advancing front of Jarrah decline (caused by Phytophthora cinnamomi). One participant reminded the cyber audience that there are varying degrees of susceptibility or tolerance among Coast Live Oaks in California forests.

Managing worldwide spread
Three different lines of discussion ensued on this subtopic. The concern over transmission of the SOD pathogen, Phytophthora ramorum, via infested growing medium or propagative material of the nursery trade was underscored. The spread of P. ramorum in the forested landscape by human visitors (e.g., mushroom collectors, recreationists, forestry workers) was discussed at length. Two additional discussion threads concerned risk assessment. The risk of P. ramorum introduction into new areas and the need for agencies or institutions to be prepared to deal with such occurrences were highlighted. Furthermore, the role of risk assessment in stopping the spread of SOD by preventing new introductions of the pathogen was discussed by several participants.

Open Topics -- Session III 
Gerard van Leeuwen, moderator

Several topics were discussed in this 'Open topics' session.

Role played by Phytophthora ramorum in SOD. Oak decline may be due to pollution, ozone, stress, and/or other factors. One participant stressed that certain 'good' climatological conditions predispose trees to become more susceptible, and that in his opinion the coast of central California offers the best of these environmental conditions, with the right amount of moisture and mild climate. Some other participants focused on the effect of the soil environment, acid rain, or air pollution (ozone) on oak decline. They referred to the symptoms of 'general' decline of oak trees, in which the pathogen P. ramorum often is not involved. This decline seems to be related to growth in very acidic soils. Another participant pointed out that predisposing factors have been investigated with SOD from the start. He stated that air pollution and other abiotic influences might affect tree health, and predispose trees to all kinds of biotic agents. The coastal forests of California however, appear to be among some of the least impacted forests by air pollution in the USA.

Relationship of Brenneria quercina and dripping cankers. Possible involvement of the bacterium Brenneria (Erwinia) quercina in dripping cankers where P. ramorum could not be isolated. Brenneria quercina was isolated from bark cankers of oaks in Spain with decline symptoms and internal necrosis.

The possible need for a new common name. Why use the abbreviation SOD when oak death is not sudden? New names proposed were 'bleeding oak canker' (but this seems to also occur with other Phytophthora's involved). Most people found it awkward to speak of SOD as the pathogen infects many non-oak hosts as well ('Ramorum leaf spot' or 'Ramorum dieback' may be better).

Control of P. ramorum. One participant stressed the need to not put all hope in chemical control. Predisposition will play a more and more important role as we move into further phases of the epidemic. The most susceptible trees will go first, and predisposition may play a more important role in the remaining, supposedly more resistant trees. From research it was shown that phosphites could be beneficial in specific cases. Another participant brought up the issue of fungicides masking effects. Infected plants treated with fungicides might be inspected and found disease-free, and then the disease might be expressed after long-distance movement of the plants.

Difference between the SOD situation in USA and Europe. In Europe, SOD is mainly a nursery problem, but in the USA it is mostly prevalent in forest environments. Can we expect similar problems in Europe? The major role of predisposition (increased soil acidification) was again discussed ('are we looking at the right suspect?'). Others brought up the importance of inoculum pressure; in California, bay laurel (Umbellularia californica) produces vast numbers of conidia on infected leaves, and oak trees in the environment subsequently get infected. In Spain, researchers are determining the sporulating capacity of potential hosts present in European forest landscape.