Epidemiological Aspects of Phytophthora Ramorum in Redwood Forests of the Coast Range of California: a 3-Year Look1

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Epidemiological Aspects of Phytophthora Ramorum in Redwood Forests of the Coast Range of California: a 3-Year Look1

The proceedings of the sudden oak death second science symposium: the state of our knowledge Epidemiological Aspects of Phytophthora ramorum in Redwood Forests of the Coast 1 Range of California: A 3-Year Look Patricia E. Maloney2, Shannon C. Lynch2, and David M. Rizzo2 Abstract Understanding the epidemiology and disease dynamics of Phytophthora ramorum in redwood forest communities will allow researchers and land managers to predict the effects on forest structure, as well as other key ecosystem processes. As part of a long-term study on the epidemiology and ecology of P. ramorum in redwood forests, 120 plots were established and censused yearly since 2002. The main hosts and tree species are coast redwood (Sequoia sempervirens), tanoak (Lithocarpus densiflorus), and bay laurel (Umbellularia californica). Baseline disease incidence across the 120 plots was 17 percent in the initial sampling in 2002. Overall disease incidence on the plots increased in 2003 and 2004 to 24 and 29 percent, respectively. This was an increase by 42 percent in 2003 and only 19 percent in 2004. We have also found that mortality rates of tanoak have been elevated in P. ramorum-infested locations as compared to uninfested locations. The number of new, individual host trees becoming infected has declined, but new infections are still occurring. Explanations for increases, decreases or leveling off may be a function of pathogen and host biology, as well as interannual variation in climate affecting P. ramorum sporulation and dispersal. Mortality rates and rates of disease increase are discussed further. Key words: Lithocarpus, tanoak, disease ecology, disease progression 1 An abstract of a poster presented at the Sudden Oak Death Second Science Symposium: The State of Our Knowledge, January 18 to 21, 2005, Monterey, California 2 Department of Plant Pathology, University of California, Davis, California 95616; [email protected] 527 .

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Research on the Epidemiology, Ecology and Management of Phytophthora Ramorum in California Forests1
Research on the Epidemiology, Ecology and Management of Phytophthora ramorum in California Forests1 David M. Rizzo2 Key words: disease management, landscape ecology, invasive species Introduction The ultimate goal of Phytophthora ramorum research is to develop disease management strategies. To date, studies have been focused at three management levels: the individual tree, the landscape (or forest stand), and the regional to international scale (Garbelotto and others 2003, Rizzo and Garbelotto 2003, Rizzo and others 2005). I will focus my brief remarks on the forest landscape, possibly the most difficult level to implement disease control strategies (for a more comprehensive discussion see Rizzo and others 2005). From a research perspective, there are four non-exclusive areas that we must continue to focus on in order to facilitate P. ramorum management in forest stands: Put the impacts of sudden oak death in context with expected successional patterns and ecosystem processes within coastal forests For any P. ramorum management proposal to be successful in coastal California forests it must also be put into context with other management goals (e.g. timber extraction, wildlife) and threats (e.g., high fuel loads due to fire suppression, other invasive species) (Rizzo and others 2005). This requires continued study on the ecology of the invaded forests in addition to examining the biology of P. ramorum. This pathogen has invaded three broad forest types in California: mixed-evergreen forests dominated by coast live oak (Quercus agrifolia), mixed-evergreen forests dominated by tanoak (Lithocarpus densiflorus) and Douglas-fir (Pseudotsuga menziesii), and coast redwood (Sequoia sempervirens) forests. With the possible exception of the coast redwood forest type, the ecology of many coastal mixed-evergreen forests has not been well characterized (Barbour and Minnich 2000).
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USDA’s Cooperative State Research, Education, and Extension Service Web site at www.csrees.usda. gov/Extension/index.html, or consult the blue pages of the telephone book under “U.S. Department of Agriculture, Cooperative State Research, Education, United States Department of Agriculture Animal and Plant Health Inspection Service and Extension Service.” A directory of State plant regulatory officials is available on the National Plant Board Web site at www.nationalplantboard.org/ member/index.shtml. Phytophthora For more information and resources concerning ramorum: Figure 6—Employees from the Maryland Department P. ramorum, visit APHIS’ Web site at of Agriculture’s Plant Protection and Weed Management www.aphis.usda.gov/plant_health/plant_pest_info/ Stopping Division (left) and APHIS’ Plant Protection and Quarantine pram/index.shtml ■ program collect leaf samples from rhododendrons during a national survey for P. ramorum in nurseries. (APHIS photo by the Spread R. Anson Eaglin) Program Aid No. 1842 APHIS has enacted strict regulations in 15 coun- ties along the California and Oregon coastline be- The U.S. Department of Agriculture (USDA) prohibits cause P. ramorum causes significant disease in those discrimination in all its programs and activities on the basis forest environments. For nurseries, preventing the of race, color, national origin, age, disability, and where introduction and establishment of the diseases applicable, sex, marital status, familial status, parental P. ramorum causes is the best defense. status, religion, sexual orientation, genetic information, political beliefs, reprisal, or because all or part of an individual’s income is derived from any public assistance program. (Not all prohibited bases apply to all programs.) How You Can Help Persons with disabilities who require alternative means for communication of program information (Braille, large print, If you suspect that shrubs or other plants are infect- audiotape, etc.) should contact USDA’s TARGET Center at ed with P.
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