MANHATTAN, Kan. — Kansas State University plant disease and horticulture experts are urging Kansans to be on the lookout for a disease that threatens oak trees and other susceptible plants, and has now been reported to be in the state.
The Kansas Department of Agriculture announced on June 7 that the pathogen that causes Sudden Oak Death, called Phytophthora ramorum, was found in rhododendron container plants. The plants are part of a shipment distributed to Walmart stores in Kansas and one Home Depot store in Pittsburg from a supplier in Oklahoma.
Information from KDA can be found at https://www.agriculture.ks.gov/SOD.
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. Red oaks are the only sub-group that is affected by P. ramorum.
“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.
Ryan Armbrust, the health and conservation forester with the Kansas Forest Service, said that the state’s oak forests are primarily located in the eastern third of the state and “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.”
“Unfortunately,” he adds, “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 trunk of oak trees, leading to a decline of the tree. Underneath the bark, the cankers have defined margins with a reddish-brown color.
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 more dry than the eastern half of the state, “but there is still a risk,” she said.
Officials at K-State and the KDA say 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.
The U.S. Department of Agriculture’s Animal and Plant Health Inspection Service maintains the most current list of plants that are susceptible to Sudden Oak Death.
Kansans can also contact their local extension agent or call the Kansas Forest Service at 785-532-3300.
— Pat Melgares, K-State Research and Extension
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