Updated at 12:45 p.m. Friday to add that the pathogen has been found in Missouri, as well.
A pathogen that’s deadly to some native trees has been found in 10 Illinois counties, including St. Clair and Monroe.
Agricultural officials found Phytophthora ramorum, which causes sudden oak death, on some ornamental plants from big-box garden centers around the state. The pathogen causes dark brown spots on the leaves and branch tips of rhododendron, azalia and lilac, but it is deadly for oaks and certain other tree species.
“There’s no cause for panic just yet,” said Diane Plewa, director and diagnostician at the University of Illinois Plant Clinic, adding that officials have not found the plant disease in any oak trees yet.
Investigators first discovered the pathogen on rhododendrons at a Walmart in Indiana. The infected plants came from nurseries in the Northwest and were distributed from Parkhill Plants in Oklahoma. Eighteen states, including Illinois and Missouri, received infected plants.
The Illinois Department of Agriculture and the U.S. Department of Agriculture are working together to find and account for all the plants carrying the pathogen.
Plewa said impacted plants could include rhododendrons or lilacs purchased in 2019 from Walmart, Hy-Vee or Rural King that show symptoms. She added plants must fit all of that criteria, since the symptoms of brown spots on leaves are common from other problems, such as a harsh winter.
Illinois Department of Agriculture Plant and Pesticide Specialist Supervisor Scott Schirmer said even though the pathogen has made its way to the state, that doesn’t mean it will take root. He compared the situation to flu season.
“We have the influenza virus floating around all over the place, but it doesn’t become the flu until it’s in a person,” he said. “The pathogen is here. It hasn’t gotten into oak trees yet.”
Agricultural officials intend to keep it that way and block it from establishing in the region. Schirmer said the pathogen moves easily through soil and water, but Illinois’ climate may stymie it.
“From a biological standpoint, there is potential hope that this pathogen won’t be able to survive in Illinois,” he said. “It is primarily thriving on the West Coast.”
Plewa agreed and said assessment maps show that most areas in the state are lower risk.
“We don’t tend to have native forested areas that would have the hosts that are the most susceptible to this disease,” she said. “The biggest concern would be if this pathogen escaped into, let’s say, the Appalachian Mountain region, or some of the native forests further east.”
The Missouri Department of Agriculture confirmed Thursday that the state also received infected plants. The plants have “Park Hill Plants” labels and were sold at Walmart and Rural King stores throughout Missouri between March and June.
Specific plant varieties that tested positive for the pathogen include: Cat Cunningham Blush, Firestorm, Holden, Nova Zembla, Percy Wiseman, Roseum Elegans, Wojnars Purple, Common Purple Lilac and Persian Lime Lilac.
Officials urge residents to dispose of infected plants immediately to stop the disease from spreading. The Missouri Department of Agriculture said consumers should not mulch, compost or dispose of any infected plants in municipal yard waste. Residents should contact the department’s Plant Pest Control team at 573-571-5505 if they notice symptoms.
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