North Central Research Station

American elms that once lined the residential streets of the Midwest have been devastated by Dutch elm disease caused by an exotic invasive pathogen. 
 Photo by J. O'Brien

The issue

Diseases resulting from the introduction of exotic pathogens into North American forests have significantly changed landscapes, impacted productivity, and put native species at risk. Populations of tree species such as the American chestnut, American elm, and butternut have been declining for many years as a result of diseases caused by invasive exotic pathogens. Several species of oaks in California are dying from a recently introduced pathogen responsible for Sudden Oak Death (SOD). Native invasive pathogens also cause serious diseases in both rural and urban areas of our region and warrant management to reduce their impacts. Some diseases caused by native invasive pathogens, such as red pine shoot blights, are increasing as a result of changing forest management in the Midwest. High value oak trees in rapidly urbanizing areas are particularly vulnerable to oak wilt, another disease caused by a native invasive pathogen.