Each summer, a few more American elm trees succumb to a widespread fungal pathogen known as Dutch elm disease. Sadly, prevention is costly and not guaranteed to protect the tree. Treatment is possible in trees that have just begun to show signs of the disease, but it is also expensive and not guaranteed.
American elm trees that die from Dutch elm disease should be removed and the wood destroyed as soon as possible to prevent further spread of the disease. Burning, burying, chipping or grinding the wood are all acceptable methods of disposal. Wood that is intended for burning needs to be destroyed immediately rather than waiting in a woodpile for cooler weather.
Leaves of infected trees typically yellow and then wilt. Yellowing starts at the branch tips and moves rapidly throughout the tree.
Lawrence residents Dale and Marilyn Kurtz first became concerned about their elm tree when they noticed yellow leaves this spring.
“It was like it was fall for the tree,” Marilyn Kurtz says. “The leaves started turning colors and dropping.”
Although the Kurtzes are unsure about how old the tree is, they know it was part of a farmstead that existed prior to the development of their neighborhood.
When the Kurtz’s elm’s leaves continued to yellow, Dale brought a few branches in to the Master Gardener Hotline at the K-State Research and Extension office in Douglas County. The only way to confirm the disease is through a laboratory test, so the Master Gardeners and I sent the sample to plant pathologists at K-State for testing. They confirmed presence of the disease after about 10 days.
Marilyn sighed when she heard the news. “I hate for this to happen to it. I guess we are probably lucky it didn’t happen sooner.”
Dutch elm disease was first identified in Kansas in 1957 and has been in the United States since at least the 1920s. Most of the American elm trees were killed in the initial waves of the disease’s spread. Elms that remain are often in isolated areas and a few more die each year.
“It was a lot of shade,” Marilyn Kurtz says regretfully. “The Baltimore orioles built their nest in it, and it’s the one we had the squirrel feeders on. We’ll have to move those now.”
Branch samples to test for Dutch elm disease need to be 1 to 2 inches in diameter and about 6 inches long. They should be taken from a part of the tree that is showing yellowing but is not completely dead. The laboratory charges $5 to cover the cost of materials used for the test.
Dutch elm disease is caused by a fungus that grows within the tree’s vascular system. As the fungus grows, it blocks water from reaching plant cells. The fungus is spread from tree to tree by two species of beetles that feed in elm trees. The disease is also spread when roots of elm trees growing near each other graft together.
Siberian elms (often called Chinese elms) are resistant to Dutch elm disease but have other disease problems and typically are structurally weak trees. True Chinese elms, sometimes called Lacebark elms, are also resistant and are more desirable than Siberian elms.
Hybrid elms that are resistant to Dutch elm disease are available, but have not been tested for long-term performance in our region.
— Jennifer Smith is the Horticulture Extension Agent for K-State Research and Extension in Douglas County. Contact her or an Extension Master Gardener with your gardening questions at 843-7058.