Dutch Elm Disease was first discovered in 1921 in the Netherlands by Dutch phytopathologists, Bea Schwarz and Christine Buisman. The name, therefore, refers to its identification origin. It’s not actually a disease confined only to the Dutch Elm Hybrid. While it was first noted in the U.S. in Ohio in 1930, by the 1980s, you could find it widely spread through most of the United States. This wilt disease is caused by the fungus Ceratocystis ulmi. While it poses a very real threat to American Elms everywhere, there is still no known cure despite decades of study on the disease.
How to Spot It
Unlike some other diseases that can take months—or even years—to fully manifest, symptoms of Dutch Elm Disease present rapidly over the course of 4-6 weeks following a tree’s leaves reaching full size. The initial symptom is called, “flagging.” When this happens, the leaves will start to yellow, then turn brown as they wilt. The flagging doesn’t effect the whole tree at once, however. It starts with one branch first. As the leaves from that branch drop, the disease spreads to nearby branches and then, eventually, the entire tree. The final result is that the tree wilts and dies. While the initial symptoms present quickly, the spread of the disease throughout the rest of the tree can take a whole season or, in some cases, a few years. That said, the only conclusive way to diagnose Dutch Elm Disease is through a lab test to confirm the fungal pathogen.
The Life Cycle
The Ceratocystis ulmi fungus depends upon insect-vectored transmission to cover long distances tree by tree. In North America, there are two insect vectors for this fungus: The European Elm Bark Beetle and the more common American Bark Beetle. These beetles get under the bark of living, or recently dead, elm trees and logs to feed and multiply. As they do this, they carry the spores from the fungus in infected trees to new, healthy trees. The life cycle of the insect vectors, then, dictates the cycle of infection by the fungus. Mature beetles can fly up to 1/4 mile when looking for new trees in which to feed or reproduce, but they can also be carried across further distances by wind. In addition to being spread by beetles, Dutch Elm Disease may also be spread from a diseased tree to a healthy one if the roots systems of the two trees overlap via a root graft.
1. There is no cure for Dutch Elm Disease. That said, the first step in caring for a tree is to look for the aforementioned flagging. If you see it, cut down a few small branches and check the sapwood for brown streaking. If that streaking is present, you should seek out a lab test to confirm whether it is actually Dutch Elm Disease. In some cases, other canker and wilt pathogens in elms can present similar symptoms. Knowing what disease you have is key in treatment strategy.
2. Keep the tree as healthy as possible. This means plenty of fertilizer and water, but be careful not to apply too much. In some (mild) cases, if there is less than 5% of the tree infected, the tree may respond to simply removing the diseased section(s) of the tree. Additionally, you need to control the insect vectors to limit spread. One proven option is to inject systemic fungicides every 1-3 years. If you consider this option, you should consult with a tree specialist (arborist) first to ensure the right amount of application for your situation.
3. Tree removal. Nobody likes to remove trees, but in some cases, it is necessary to preserve the health of neighboring trees. That said, the wood from the removed tree should not be stored for firewood. It needs to be chipped in order to completely destroy the beetle’s breeding grounds. Also, as mentioned, the disease may be spread through root grafts of neighboring trees, which may require the mechanical severing of those root grafts to help slow the spread if it can be done before the fungus spreads from an infected tree to a healthy one. That said, destruction of the root graft may not always be a pragmatic option in a home setting. Again, this is a time to consult with a tree specialist.
4. Replace the trees. The final, and perhaps most obvious option, is to replace the trees. If you like the look of elm trees, there are still some elms that are resistant to Dutch Elm Disease. One option, with a shape that is quite similar to the American Elm, is the Japanese Zelkova. Another option is the Chinese Elm (Ulmus parviflora), which is often noted for its multi-color bark. Remember, while both trees are resistant to Dutch Elm Disease, that does not mean they are immune to it.
More and more, homeowners are looking for organic options for a variety of different reasons. That said, options 1, 3, and 4 mentioned above are organic. Further, option 2, sans the fungicide, is also an organic option for combating Dutch Elm Disease.
At E.P.M LawnScape and Supply, we offer a host of professional tree and shrub care services. If you have concerns about your trees and/or landscaping, feel free to contact us online or call us at (517) 990-0110 today.