The American elm, Ulmus americana, is a beautiful, long-lived, and fast-growing tree, however, its popularity and population have decreased since the introduction of Dutch elm disease (DED) in the 1930’s. The American elm was one of the most popular street trees in its native range. Streets lined almost exclusively with elms were eventually decimated by DED. After the initial die-off, some trees survived, but these trees are still susceptible to the disease and outbreaks are common from time to time. Dutch elm disease is a fungal wilt disease that affects all native elms in Kansas. This disease is lethal to elms although some trees take longer to succumb to the disease than others. Fungal spores carried by native and non-native elm bark beetles infect trees in the spring.
Symptoms of Dutch Elm Disease
Symptoms typically occur in late May and sometimes August or September. Small limbs near the top of the tree begin to wilt and leaves appear off-color (usually a light green instead of a dark green) and then turn yellow and brown. The fungus plugs the vascular system as it spreads through the tree causing the wilting symptoms to spread. Other diseases such as elm yellows can cause yellowing of the leaves which look similar to DED. Examine sapwood for streaking to differentiate the diseases. Dutch elm disease will cause brown streaks in the sapwood.
In addition to being spread by beetles, this disease can be spread through root grafts. An infected tree in close proximity to a healthy elm can infect the healthy tree. Elms should be removed and destroyed if confirmed to have this disease. Do not save firewood from these trees because they harbor bark beetles and infection.
Prevention of Dutch Elm Disease
Prevention of DED is key to saving prized elms. Trees can be saved if less than 25% of the canopy is infected, but the likelihood of survival is low and treatment cost is high. Dutch elm is easy to prevent with a fungicide injection into the root flares of the tree. The protection from these injections lasts for three years.
If you are concerned about the health of your elm, you can contact us, we would love to help you make a plan to save your beautiful trees.