Modeling the Introduction and Establishment Risk for Phytophthora alni in the United States

Marla C. Downing, Thomas Jung, Vernon Thomas, Markus Blaschke, Michael F. Tuffly, and Robin Reich

USDA Forest Service Forest Health Technology Enterprise Team; Consultant for forest and tree diseases; Information and Technology Experts, Inc. (ITX); Bavarian State Institute of Forestry; ERIA Consultants, LLC; and Colorado State University 

Increases in anthropogenic transportation of commodities in the last 200 years have led to the international spread of Phytophthora pathogens.  For example, the European species Phytophthora ramorum has recently caused tremendous damage and mortality to Quercus and Lithocarpus trees in California.  To address concerns and gain information about the potential spread of additional Phytophthora species, the USDA Forest Service, Forest Health Technology Enterprise Team (FHTET), in Fort Collins, Colorado, is assessing the risk of introduction and establishment of Phytophthora alni into the U.S.  P. alni is a water-borne disease that is currently known to occur only in Europe on alder (Alnus) trees.  It has spread throughout Europe via rivers, a natural dispersal mechanism for the pathogen, and through the common nursery practice of irrigating field stock with river water.  The P. alni pathogen can adhere to the bare roots of non-host nursery stock and is capable of surviving transportation to the U.S. Therefore, to assess the risk of introduction of P. alni to the U.S., FHTET has developed a model that considers the importation of European nursery stock to U.S. wholesale nurseries and the natural dispersal mechanisms for the motile zoospores: streams and rivers.  FHTET is currently developing an establishment model. First by assessing the presence or absence of P. alni in Germany using climate, elevation, slope, aspect, landform, soil, river, flood, and satellite data in a classification tree, a non-parametric statistical technique.  Then the German model will identify the parameters that will be used to model the potential establishment of P. alni in the U.S.  The product of the introduction and establishment surfaces will describe the overall national susceptibility.

Exotic Pests Session - Tuesday Afternoon

corresponding author:

Marla C. Downing
USDA Forest Service
Forest Health Technology Enterprise Team
2150 Centre Avenue, Bldg. A., Suite 331
Fort Collins, CO 80526-1891
970-295-5843
mdowning@fs.fed.us