Sudden Oak Death and Ramorum Blight, caused from the pathogen Phytophthora ramorum, has been detected on ornamental plants in multiple Midwest states due to a shipment from an infected supplier. In Illinois, it has been detected on multiple varieties of Rhododendron, sold in some Walmart, Rural King, and Hy-Vee stores across the state.

People who are concerned about possible infected plants can call your local University of Illinois Extension office or the Illinois Department of Agriculture. There are three questions that determine if your Rhododendron plants are at risk:

1. When were the plants purchased? If the plants were not purchased in 2019, it is unlikely that they are infected.

2. What are the plants? While the disease has a very wide host range, currently only rhododendron and lilac plants shipped to the Midwest have been confirmed as being infected. If the host is something other than a rhododendron or lilac, it is less likely that they are infected.

3. What symptoms are the plants displaying? Ramorum blight in woody ornamentals can look a lot like bacterial blight (especially on lilacs) and winter injury (especially on rhododendrons). Dark, chocolate-brown lesions on the leaves and terminal tip dieback with dark brown lesions on the stems are classic symptoms of this disease. Wilting and brown or black discoloration on trunks can also occur.

While this is certainly a concerning situation, there is no reason to panic just yet. The pathogen causes two diseases, depending on the host: Ramorum blight on many ornamental plants, and Sudden Oak Death to oaks. There is no evidence that oak trees have been infected in Illinois, and the fact that the infected plants were detected quickly minimizes the possibility of this pathogen escaping into the environment.

If you suspect that a plant may be infected with Phytophthora ramorum, please contact the Illinois Department of Agriculture at 815-787-5476 or Scott.Schirmer@Illinois.gov. Please include the host and variety if known, and the year and location of purchase. Because this is a regulated pathogen, do NOT destroy the plant without the approval of the Department of Agriculture. This pathogen can spread through irrigation water, so we recommend either not irrigating possibly infected plants, or watering at the base of the plants (try to avoid wetting the leaves or creating irrigation runoff). Sanitize any tools or equipment that may have come into contact with suspect plants (10% bleach or 70% ethanol solutions work well for most situations).