Local experts are on a learning curve after the Indiana Department of Natural Resources confirmed that more than 70 Walmart stores and 18 Rural King stores in the state have received rhododendron plants infected with sudden oak death, a fungal pathogen that kills oak trees.

“According to purchase/shipment records, Allen and our surrounding counties received shipments of rhododendrons known to have come from an infected nursery,” according to a statement from Derek Veit, Fort Wayne Parks and Recreation’s superintendent of forestry operations. “Infected host plants will be destroyed.”

Megan Abraham of the IDNR Division of Entomology and Plant Pathology, confirmed that in an email.

“Yes stores in Allen County received material in their Walmarts and Rural Kings,” she wrote. “Our inspector in that area is following up and removing infested materials from the shelves.”

According to a statement from the DNR, workers from the state Department of Entomology & Plant Pathology have been visiting stores across Indiana to destroy any stock that has been found infested and quarantine any stock that is symptomatic. The division said it has made this its top priority.

The DNR has destroyed approximately 1,500 infested rhododendron so far and pulled another 1,500 from stores. The DNR has ordered these stores to stop selling rhododendron until further notice. Any quarantined material not infected will be released after testing at Purdue University.

The DNR originally reported May 22 that it had intercepted plants with the fungal pathogen for the first time in about 10 years in Columbus, Noblesville, South Bend, Sullivan and Tippecanoe.

The DNR is following up with homeowners who have called in to say they’ve purchased material that they believe is infested or are seeing signs or symptoms of sick trees in the environment.

Sudden oak death has killed large tracts of oaks on the West Coast. Sudden oak death has not been established in the Midwest, to date. It can kill standing oak trees, which could happen if SOD-positive rhododendron were planted within about 6 feet of a standing oak.

Sudden oak death travels in more than a hundred species of host plant material. It causes some browning of the leaves in the host but does not kill it.

The threat comes a few years after the area saw devastation of its ash trees from the emerald ash borer.

Veit said, “The emerald ash borer reinforced the importance of maintaining a diversified urban canopy. Fort Wayne Parks and Recreation has been working toward a 10-20-30 species diversity goal. The 10-20-30 rule is a guideline intended to reduce the risk of catastrophic tree loss due to circumstances such as this pathogen. The guideline suggests an urban tree population should include no more than 10% of any one species, 20% of any one genus, or 30% of any family. It is aesthetically pleasing to plant similar tree species in defined spaces. This guideline is used as a measuring stick to evaluate our urban canopy as a whole.”

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