Dutch elm disease

An elm tree is both a deciduous and semi-deciduous tree commonly found in places like Japan, Indonesia, Mexico, and Siberia. It is valued because of its interlocking grain and the resistant to splitting and decay. The wood is used for creating wheels, chair seats, water pipes (during the Medieval time), and coffins. ^{(1, 2, 3)}

What is a Dutch elm disease? It is a vascular wilt disease characterized by wilting and yellowing of the leaves of the plants. Eventually, the leaves turn brown and curl up causing the branches to die. It affects some of the parts of the plant but eventually, the symptoms will progress throughout the crown. The plants/trees will eventually die. ^{(2, 3)}

Image 1: A healthy elm tree.
Picture Source: upload.wikimedia.org

Picture 2: An American elm tree.
Photo source: www.thetreecenter.com

What is the cause of a Dutch elm disease?

It is caused by Ophiostoma-ulmi, which is a pretty aggressive type of fungus. It can kill the tree, even the healthiest elm tree. It invades the water transport vessels and produces toxins. In return, the tree blocks the fungus thereby preventing water to flow through the different parts of the trees causing the leaves and branches to wilt and dry. ^{(2, 3, 4)}

Photo 3: The trunk of a tree with a Dutch elm disease.
Image Source: upload.wikimedia.org

Image 4: Wilted and discolored leaves of a tree with a Dutch elm disease.
Picture Source: c1.staticflickr.com

Picture 5: A closer look at the female elm bark beetle.
Photo Source: encrypted-tbn0.gstatic.com

How is Dutch elm disease spread?

The fungus that causes Dutch elm disease can be spread in two ways:

1. Female elm bark beetles – The beetles lay eggs beneath the bark of the affected elm trees and the hatched beetles will then be carrying the deadly fungus on their bodies. The carrier beetles will fly to other elm trees thereby spreading the infection. What’s even scarier is that thousands of beetles can hatch from a single elm tree.
2. Roots of two or more elm trees – when trees grow near each other, there is a tendency that the roots get in contact and graft together thereby providing the fungus an opportunity to spread the infection. ^{(4, 5, 6)}

Dutch elm disease symptoms

The symptoms of Dutch elm disease is evident sometime last week of June to the middle of July. Early signs and symptoms include wilting of the leaves and eventually, the leaves will turn brown. The leaves will droop, turn to yellow, and fall off in the late summertime. The sap of the wood will have an obvious brown staining which is visible if you remove the bark of the infected twigs. ^{(6, 7)}

Dutch elm disease treatment

There are various ways to treat, manage, and prevent Dutch elm disease. Some of the tested and proven effective ways to manage, cure, and prevent Dutch elm disease are as follows:

• Cultural practices can significantly help in preventing the spread of Dutch elm disease. Some of the cultural practices used are avoiding monocultures of elm trees, getting rid of the dead branches, cut wood, and trees.
• If the elm trees are close to each other, the root graft should be broken so as to prevent the spread of infection.
• It is important to carefully check the elm trees to detect the signs of infection the earliest time possible.
• The infected tree that had eventually died should be buried, chipped, or even burned to make sure that it will not be a home for female elm bark beetle.
• A fungicide is injected into the infected elm tree. As a matter of fact, elm trees that are at risk for infection can be infected with fungicide too. However, fungicides can be extremely expensive. So, what most people do is they use chemicals to protect high-value elm trees.
• If you are looking for a long-term solution for Dutch elm disease, the best thing to do is to develop disease-resistant cultivars of an elm tree. ^{(8, 9, 10)}

What to keep in mind?

As someone who has an elm tree, you have to be aware that up until now there is no definite cure for the disease. What you can do though is to make sure that your plants are in their best form. Keep them healthy by watering them regularly and use high-quality fertilizer. If less than 5% of your plant is infected, then it could respond well to pruning. If the tree is severely infected, the best thing to do is to remove the diseases/infected trees. You might be thinking of using the wood for a firewood but doing so can just spread the infection. You have to chip the wood to prevent the beetle from making the wood a breeding place. The diseased elm trees should be replaced by a variety that is resistant to Dutch elm disease. One of the best choices is the Ulmus parviflora, the one that has a multi-colored bark. Other great choices include Zelkova serrate and Japanese zelkova. ^{(1, 5, 9)}

References:

1. https://en.wikipedia.org/wiki/Elm
2. https://www.sciencedaily.com/terms/elm.htm
3. https://en.wikipedia.org/wiki/Dutch_elm_disease
4. https://www.apsnet.org/edcenter/intropp/lessons/fungi/ascomycetes/Pages/DutchElm.aspx
5. https://www.extension.umn.edu/garden/yard-garden/trees-shrubs/dutch-elm-disease/
6. https://www.forestry.gov.uk/fr/hcou-4u4jcl
7. https://www.britannica.com/science/Dutch-elm-disease
8. https://www.rhs.org.uk/advice/profile?PID=154
9. http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/prm1043?opendocument
10. https://www.ontario.ca/page/dutch-elm-disease