Released August 27, 2009
MANHATTAN, Kan. – Several samples tested positive for Dutch elm disease this summer at Kansas State University’s Plant Disease Diagnostic Lab.
Carried by two species of elm bark beetle, the disease first entered Kansas in 1957 and soon cut a wide, deadly swath through the state’s American, rock, slippery and cedar elms. Even so, it finds additional elms to kill every year, said Megan Kennelly, plant pathologist with K-State Research and Extension.
“Fortunately, we know more about DED now and can prevent it through sanitation and pruning. But, early action is vital,” Kennelly said. “For people who want to try them, systemic fungicide injections are available now, too. A trained arborist has to administer the injections every three years. The cost each time can be several hundred dollars for the fungicide – plus labor – so it tends to be used as a preventive only for important landscape trees.”
Still, pruning alone can save trees in the first stages of a beetle-spread infection, she said. Typically, the first symptoms are yellowish, wilted leaves on branches high in the tree crown.
“DED causes brownish-red streaking in the sapwood, too. You check for that by peeling back the bark on a wilted branch. If you find it, then you cut off the branch 10 feet below the lowest sign of streaking,” she said. “Naturally, you also disinfect your tools between cuts and monitor the tree for further wilting.”
Unfortunately, elm roots tend to fuse together if trees are within 50 feet of each other, Kennelly said. And, a “shared” root system can be an even quicker route for the spread of Dutch elm -- which is why the disease was so devastating at first in urban areas. Closing that kind of access requires digging a trench 24 inches deep to sever the fused roots halfway between an infected elm and its neighbors. Then the removed soil can go back into the trench.
If wilt occurs in more than 25 percent of a tree’s crown, however, the disease is basically unstoppable, she warned. And, whether dying or dead, infected elms should be buried, chipped or burned as soon as possible – and not stored as firewood. They’re a reservoir for the disease fungus and an egg-laying site for the bark beetles.
Homeowners wanting specific help in identifying Dutch elm disease can collect several recently wilted branches, one-half to 2 inches in diameter. (Dead branches won’t work.) They can submit this sample to their nearest county or district Extension office for forwarding to K-State’s diagnostic lab.
More information about Dutch elm disease is available on the Web under “Common Plant Problems in Kansas” at http://www.hfrr.ksu.edu/DesktopDefault.aspx?tabid=586.
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http://www.ksre.ksu.edu/ksrenews/story/briefs082709.aspx
Editor: Elaine Edwards, elainee@ksu.edu
