Invasive Pathogen Update from Illinois' Home, Yard, and Garden

by Nancy Pataky, UI Plant Pathologist

Invasive species are species that are nonnative to an area and whose introduction is likely to cause economic or environmental harm or harm to human health. The invasive species could be a plant, an animal, or other organisms. For more information, visit the site: http://www.invasivespeciesinfo.gov/.
Plant diseases are caused by pathogens, which are categorized as “other organisms” in the definition above. Ramorum blight is an example of a plant disease caused by an invasive plant pathogen. This disease is also known as sudden oak death and is a threat to the oak forests of the eastern United States. Basic facts about Ramorum blight are discussed in issue no. 1 of this newsletter. Ramorum blight is caused by a pathogen called Phytophthora ramorum; and issue no. 12 compares this disease with other Phytophthora diseases.
Ramorum blight was first confirmed in the United States in 1995, when it was found in California. In 2005, it had been identified in 22 states; but measures to prevent its establishment and spread outside of the West Coast have been intensified. The updates for 2006 have to do with a confirmation of this disease in the Midwest and changes in known hosts.
In August 2006, Ramorum blight was confirmed in Portage, Indiana, on viburnum plants shipped from Oregon. Steps were taken immediately to contain and destroy infected plants, and it has not been found elsewhere in Indiana.
Illinois Department of Agriculture inspectors participated in the national nursery survey of Phytophthora ramorum for the past 3 years. In 2006, 97 nursery samples were submitted to the University of Illinois Plant Clinic and tested for the presence of Phytophthora, using ELISA (enzyme-linked immunosorbant assays) tests. To date, Phytophthora ramorum has not been detected in Illinois.
A list of Phytophthora ramorum hosts is kept by USDA–APHIS (United States Department of Agriculture, Animal and Plant Health Inspection Service) and frequently updated. In April 2006, there were 100 host plants. As of September 11, it listed 105 plants. You can access this list at www.aphis.usda.gov/ppq/ispm/pramorum/pdf_files/usdaprlist.pdf. Review symptoms and be watchful of any plants received from the West Coast, especially lilac, rhododendron, honeysuckle, viburnum, camellia, pieris, vaccinium, Douglas-fir, white fir, and horsechestnut.