On June 7, the Kansas Department of Agriculture informed Kansas residents that Phytophthora ramorum (P. ramorum), the cause of sudden oak death, was found on rhododendron container plants in Kansas. The plants are part of a shipment to 60 Walmart stores across Kansas and one Home Depot store in Pittsburg from Park Hill nursery in Oklahoma. The Walmart in Hays was one of the stores that the infected plants were sold to. If you purchased a rhododendron from the Hays Walmart between April and June, it is very important to take action to help reduce potential spread of the disease. Homeowners who have purchased rhododendrons from these stores should dig up the plant, including the root ball, double bag it in plastic, and send it to the landfill.
Sudden oak death is a disease that can take down entire forests of oaks in very little time. The cause and cure are unknown to this day. Oaks that are most susceptible to this disease are red oaks, which are native to Kansas. The risk for Phytophthora ramorum establishment into oak plantings in western Kansas is lower than eastern Kansas because it is typically drier and there are fewer susceptible trees, but there still is risk especially with the amount of rainfall that Western Kansas has had this spring.
Long distance spread of this disease is through the movement of infected nursery plants between states. The disease can survive in infected plant tissue, soil and water, so local movement into landscapes would be through infected plant material. Spread from rhododendrons in the landscape to nearby oak trees would be through aerial splash dispersal (i.e. rainfall) or water runoff.
This is the first introduction of Phytophthora ramorum into Kansas and the Kansas Department of Agriculture, Kansas State University, and the Kansas Forest Service will continue to monitor its progress. The disease is a threat to Kansas forests and landscapes. K-State Research and Extension will be sharing information on the disease as developments occur.
You can find more information about sudden oak death at the Kansas Dept. of Agriculture Website, by contacting the Kansas Forest Service, or by contacting Lauren Walz, the Cottonwood District Horticulture Extension agent at 785-628-9430.