Infected rhododendron plants, distributed by a nursery in Oklahoma, have been sold in 10 Midwest states. Experts are recommending that gardeners dispose of all container rhododendrons that could be infected with sudden oak death disease to prevent loss of oak trees.

By Jenny Krane
June 11, 2019

Midwestern states are in a panic over rhododendrons that could be spreading sudden oak death, a plant disease that can quickly wipe out established oak trees. The infected rhododendrons have been traced back to Park Hill Plants nursery in Oklahoma, which shipped the plants to Walmart stores and select The Home Depot and Rural King locations in 10 states.

Sudden oak death is a fungus-like plant pathogen that affects many oak species and over 100 other known species like rhododendron, viburnum, and camellia. It has killed large populations of oaks and other natives in California and Oregon for the last 20 years, but it has never been established in the Midwest before this.

White oaks are not susceptible, but red and intermediate oaks can be infected. The oak species know to be the most susceptible on the West Coast (where sudden oak death has been established) are: coast live oak, California black oak, Shreve's oak, and canyon live oak. Symptoms include brown spots on leaves, red-brown trunk cankers, seeping sap, and bark splitting. The pathogen weakens the trunk of oak trees and also attracts harmful insects and other types of fungi.

‘Roseum Elegans’ rhododendron is one of the varieties that may carry Sudden Oak Death.

Indiana and Kansas are two of the states that have been hit the hardest, with rhododendrons at 60 stores in Kansas and 70 stores in Indiana. Iowa and Nebraska are in the process of investigating potential infection. Because there is no cure for the plant disease, both Kansas and Indiana officials are requesting that residents dispose of any rhododendrons purchased since April from the outlined locations.

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The Kansas Department of Agriculture identified these varieties as those that should be destroyed because of possible infection: ‘Cat Cunningham Blush’, ‘Firestorm’, ‘Holden’, ‘Nova Zembla’, ‘Percy Wiseman’, ‘Roseum Elegans’, and ‘Wojnars Purple’. These plants should be dug up (root ball included), double bagged in trash bags and thrown away. Any garden tools or shoes that came in contact with the plants should be sanitized.

According to USDA protocols, all plants within a 2-meter radius of an officially sampled and confirmed infected plant should be destroyed. A plant infected with sudden oak death disease can infect a tree if the tree is planted within 6 feet of the infected plant. You can determine if a plant is infected by looking for symptoms of brown leaf spots, wilting leaves, and stem dieback.

If you purchased a rhododendron in the Midwest in April, May or June, check your plant for signs of the disease. Call the store where you purchased the plant to see who the store's supplier is or call your local DNR extension for assistance. Remove infected bushes and surrounding plants to prevent the disease from killing oak trees in your area.

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