Mold that kills oaks found in Cook County

Shrubs sold at Walmart carried pathogen from West Coast

July 9th, 2019 12:33 PM

By Bob Uphues


A pathogen that has wiped out large numbers of oak trees in California, the Pacific Northwest and Europe has been found in Cook County and other locations in the state of Illinois, the state's Department of Agriculture announced last week.

Phytophthora ramorum, which causes the disease Sudden Oak Death, has been traced to rhododendron and lilac bushes sold at 10 Walmart locations in Cook, Jackson, Jefferson, Lee, Macon, Monroe, St. Claire, Stephenson and Will counties and at a Hy-Vee store in McDonough County.

According to Scott Schirmer, spokesman for the Illinois Department of Agriculture, the Walmart locations in Cook County where infected plants were identified were in northwest suburban Rolling Meadows and south suburban Richton Park.

"There have been a lot of sites identified as far as retail locations, but as of now it's early and we haven't had many reports or calls yet," said Schirmer. "We're trying to get resolution on where they were planted and how they look in the landscape."  

If anyone has bought rhododendrons from Walmart and if those plants are in poor condition, they are being asked to contact the Illinois Department of Agriculture's DeKalb office at 815-787-5476 or the University of Illinois Extension office in Westchester at 708-449-4320.

Sudden Oak Death has not been confirmed in any oak trees in the state of Illinois, although they are susceptible to the pathogen. The disease is incurable, according to the IDOA in trees although it poses no threat to humans, pets or other food sources.

According to the California Oak Mortality Task Force, which operates the website, the pathogen Phytophthora ramorum has been identified as affecting more than 100 species of trees, shrubs and other plants. Symptoms on trees include bole or trunk cankers, while shrub symptoms include leaf spotting and shoot dieback.

"Trunk cankers are the most damaging, and often lead to death," the website states.

Introduced to California in the mid-1990s, the pathogen has killed millions of oaks in that state, according to the California Oak Mortality Task Force.

The pathogen travels well through soil and water, which is why state officials want to quickly quarantine and remove any infected plants.

Michael Collins, the village forester in Riverside, said the pathogen most likely would attack tree root systems, exploiting any wound in the plant.

"If you've purchased any plants from Walmart this past spring, reach out to the IDOA," Collins said. "And you can certainly let us know as a head's up."

Oak trees represent about 20 percent of Riverside's public tree stock, said Collins, amounting to roughly 2,000 trees.

"The main idea is to get ahead of this and quarantine plants infected by the fungus," said Collins, who added that residents who use landscape contractors might want to contact them to see where they bought their plants.

It's unclear how many oaks are on public lands in Brookfield. The village's forestry department continues to update its inventory, but the village has been planting more oak species in recent years, according to Victor Janusz, the village's forester. There's also the oak savanna on the north end of Kiwanis Park.

North Riverside has 216 oak trees on public land, said Public Works Director Tim Kutt, not counting forest preserve property.

The rhododendron and lilac plants identified in Illinois, according to Schirmer, have been tied to a particular shipment of plants from the state of Washington in April or May. Those plants were sold to Walmart through a company called Parkhill Plants in Oklahoma. Those shipments also included plants from British Columbia, but Schirmer said the Canadian plants have not been identified as carrying the pathogen.

According to a press release issued by the Department of Agriculture on July 2, the shrubs routed through Parkhill Plants were distributed in 18 states.

Sale of those plants has been halted, according to the IDOA, which has also collected infected plants in order to dispose of them.

The press release states the following varieties have tested positive for Phytophthora ramorum:

Rhododendrons: Cat Cunningham Blush, Firestorm, Holden, Minnetonka, Nova Zembla, Percy Wiseman, Purpureum Elegans, Roseum Elegans and Wojnars Purple.

Lilac: Common Purple and Persian Lime.

While there have been no cases of Sudden Oak Death identified in Illinois yet, said Schirmer, residents should be vigilant.

"The analogy I use is that you have the flu virus all around, but it's not the flu until it gets into a person," Schirmer said. "The Sudden Oak Death pathogen is here and could potentially lead to it."

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