Sudden Oak Death (Phytophthora ramorum)

​​​​Sudden oak death is a plant disease caused by a water mold called Phytophthora ramorum. We have not found sudden oak death or P. ramorum on the landscape in Wisconsin, and the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) is trying to prevent its introduction to the state. We have found it infrequently on imported nursery stock.

Healthy oak treeP. ramorum is causing widespread tree death in coastal forests of California and Oregon. To date this disease organism has been found in nursery stock and water bodies in at least 25 states.

Besides oak trees, more than 100 other plant species are susceptible to leaf blight infection and dieback caused by P. ramorum. These include popular ornamental plants such as rhododendron, viburnum, lilac, and Pieris (commonly known as andromeda). 

DATCP inspectors routinely check nursery stock for symptoms of infection on plant leaves, and submit suspect samples to our laboratory for testing. We also enforce a quarantine that restricts imports of wood, soil and some plants from areas of the United States that the federal government regulates for P. ramorum.

Sudden oak death symptoms are difficult for the layman to distinguish from other diseases. If you have oak trees on your property showing symptoms of leaf or bark damage, it is best to consult a certified arborist or UW Plant Disease Diagnostic Clinic.  

Please note that sudden oak death is not the same disease as oak wilt​ or oak anthracnose, which exist in much of Wisconsin. Information about oak wilt is available on the Department of Natural Resources website. Information about anthracnose​ is available on the University of Wisconsin-Extension website

Quarantine requirements

Back to main pest and disease page