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Pathogen that causes Sudden Oak Death found in Illinois

oak tree affected by Phytophthora ramorum pathogen

In 2019, the pathogen that causes Sudden Oak Death, a plant disease that has killed large tracts of oaks and affected many native plant species in California, Oregon, and Europe, was found in Illinois. 

Phytophthora ramorum, the causal agent of Sudden Oak Death (SOD) was confirmed in ornamental plants at 11 stores throughout Illinois. A total of 18 states received diseased plants. 

IDOA and USDA field staff visited sites inspecting rhododendrons as well as azalea, viburnum, and lilac. Symptomatic plants were sampled for testing and placed on stop-sale order, destroyed or relinquished to officials on site. The investigation did not detect P. ramorum on any hosts and that there is no evidence that the pathogen escaped or is established in the environment.

About the pathogen

The pathogen can cause both a blight and sudden death, depending on the host. The disease can infect more than 100 different species. Because P. ramorum has only been detected on non-oak hosts, the disease Ramorum blight has been confirmed in Illinois but not the disease Sudden Oak Death. There is no evidence that any oak trees in Illinois are infected at this point.

In general, most plants will get "ramorum blight" as carriers, however, oaks are considered terminal hosts as it can often be fatal and is incurable. 

The pathogen travels well in soil and water, so escape into the environment is a concern. Blight symptoms of the disease include, but are not limited to, foliar spots, browning or wilting leaves, tip/shoot dieback, and brown or black discoloration on stems and/or trunks.

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Learn more about Illinois invasive species

ABOUT THE AUTHOR: Diane Plewa is a Plant Diagnostic Outreach Specialist with the University of Illinois Plant Clinic.