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An oak-killing pathogen has been found in Illinois; experts are on alert

Russell Lissau
Forestry, botanical and agricultural experts in the Chicago area are on alert for a plant pathogen that has killed large tracts of oak trees on the West Coast and been detected on ornamental plants in Cook and Will counties.
Phytophthera ramorum, which causes sudden oak death, has been confirmed in plants sold at 10 Walmart stores in those and seven other Illinois counties, as well as at a Hy-Vee store in a 10th county, according to the Illinois Department of Agriculture.
Officials have found no evidence of infected oaks in Illinois. But the disease has killed oaks and affected many native plant species in California, Oregon, and Europe, state agriculture officials said.
Oaks dominate wooded areas in the Chicago area and elsewhere in the Midwest.
Lydia Scott, director of the Chicago Region Trees Initiative and manager of the community trees program at the Morton Arboretum in Lisle, said her agency has been in "close communication" with state agriculture officials about the pathogen.
"We are relieved that it has not been found in any oaks (in Illinois)," Scott said. "We will continue to be in touch with the IDOA and work with them to communicate any developments to our many partners across the state, especially public and private landowners."
Sudden oak death affects oaks and other trees and plants. An incurable condition, it can cause a blight and death, depending on the host, said Diane Plewa, a diagnostician at the University of Illinois Plant Clinic.
Blight symptoms include spots, browning or wilting leaves, and brown or black discoloration on stems or trunks.
The pathogen poses no threats to humans, pets, livestock or food sources.
Illinois and federal agriculture officials have been visiting nurseries where the infected plants originated since late May and testing plant species that can host the pathogen, including rhododendrons, azaleas, viburnums and lilacs.
The agencies are destroying or collecting symptomatic plants to prevent spread of the disease.
Cook County Forest Preserve District officials are aware of the pathogen's discovery in Illinois. Members of the district's resource management department have been trained to identify the symptoms of oak diseases, and they're on the lookout for the signs of sudden oak death, district spokeswoman Stacina Stagner said.
They're also sharing information about this and other tree diseases with state and federal officials, the Morton Arboretum and other organizations, Stagner said.
Lake County Forest Preserve District officials are constantly watching for signs of diseases like this, as well as gypsy moths or other creatures that can cause damage, said Jim Anderson, the district's director of natural resources.
The district tries to keep oak ecosystems healthy and boost their disease resistance by eliminating invasive species, keeping tree canopies open and managing growth with controlled fires, Anderson said.
People can prevent the spread of the pathogen by buying native plants grown in the area, he said. Local nurseries often are a good source, he said.
Walmart and Rural King are voluntarily pulling potentially infected plants from their stores, state agriculture officials said.
If you have sick-looking rhododendrons that were purchased at Walmart, Hy-Vee, or Rural King stores since April, contact the Illinois Department of Agriculture at (815) 787-5476 or You could also contact the nearest University of Illinois Extension office.
For more information on sudden oak death, visit
• Daily Herald Staff Writer Mick Zawislak contributed to this report.