On June 7, a pathogen that causes Sudden Oak Death (SOD), called Phytophthora ramorum, was found in rhododendron container plants in Kansas. 

SOD is a fungal plant disease that has infected and killed large sections of oaks and other native species in California and Oregon. Infected oak species or rhododendrons have been identified in 10 states in the Midwest, including Kansas. 

As the infected plants have been found in the Midwest, they have all been traced to a common source. The infected plants are known to have been a result of shipment distribution: In Kansas, one Home Depot store in Pittsburg and Walmart stores received infected plants from a supplier in Oklahoma. 

Kansas State University plant disease and horticulture experts urge Kansans to be on the lookout for this disease that threatens oak trees and other susceptible plants. These plants are to be reported to the Kansas Department of Agriculture (KDA.) 

Sudden Oak Death is not new to the United States, but this is the first time that it has been reported in Kansas. The disease has caused damage in susceptible trees for nearly 15 years, especially in California, Washington and Oregon.

Kansas oak forests are primarily located in the eastern third of the state commonly known as The Cross Timbers, which consist of native oaks. 

Red oaks are the only sub-group that is affected by P. ramorum. 

“Most native oaks like bur oak are of the potentially less-susceptible white oak group, but there are millions of red, black, pin, shumard, blackjack, shingle and other oaks that could be impacted should this disease gain a foothold in the state,” said Ryan Armbrust, health and conservation forester with the Kansas Forest Service.

“Unfortunately, few details are certain about how this pathogen might affect the species that are native to our central hardwood forests, so we encourage the public to be proactive in taking steps to ensure this disease does not spread from rhododendrons or other infested plant material into our community forests and rural woodlands.”

According to K-State plant pathologist Megan Kennelly, P. ramorum causes bleeding cankers on the trunks of oak trees, leading to a decline of the tree. Underneath the bark, the cankers have defined margins with a reddish-brown color.

On an ornamental scale, “It can also infect a broad range of nursery plants at which point it is referred to as a Ramorum blight,” said Cheryl Boyer, a nursery crop production specialist with K-State Research and Extension. Common shrubs are lilacs, azaleas and more.

Kennelly noted that on nursery plants, the symptoms are leaf spotting or browning and sometimes a stem dieback. The symptoms can be confused with common problems such as sunscald. P. ramorum rarely causes death of nursery plants.

“The Phytophthora diseases are called water molds, and they are triggered by wet conditions,” Kennelly said. “Kansas has had significant rain this spring, so conditions have been favorable for the disease.”

She noted that the likelihood of P. ramorum moving into western Kansas oak plantings is much less because that region is dryer than the eastern half of the state, “but there is still a risk,” she said.

What to do if you recently

purchased an infected plant:

Officials at K-State and the KDA said that as a precaution, homeowners who purchased a rhododendron at Walmart or the Home Depot in Pittsburg this spring should immediately dig up the plant (including the root ball), double bag it in plastic and dispose of it in the garbage.

Garden tools and shoes or boots that come into the contact with the plant or its root ball soil should be sanitized before using them in other areas of the landscape.

Contact local extension agent, Elizabeth Espino, Agriculture and Natural Resources, at (620) 221-5450 for a current list of susceptible plants and more information.

Information from KDA can be found at www.agriculture.ks.gov/SOD.

 

Sources:

Sudden Oak Death Detected in Kansas – Kansas State Research and Extension Press Release.

Sudden Oak Death- Kansas Department of Agriculture.

Elizabeth Espino is the Agriculture and Natural Resources Agent for Cowley County Extension. She can be reached at (620) 221-5450 or espino@ksu.edu.

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