Dutch Elm Disease

What is Dutch Elm Disease (DED)?

(Ophiostoma novo-ulmi)

Dutch Elm Disease (DED) is an invasive fungal pathogen that is lethal to a variety of elm tree species native to Vermont and the United States. It arrived in the U.S. in the 1930s and now can be found across nearly all of the country. The species of elms impacted include: American elm (Ulmus americana), red or slippery elm (U. rubra), and rock elm (U. thomasii). American elms are particularly susceptible to the disease, however, some varieties of American elm have a higher tolerance to the disease. These higher tolerance trees may recover if infected and are often marketed as DED resistant.

How is DED spread and what does it do?

DED is primarily spread to host trees by elm bark beetles (the native elm bark beetle (Hylurgopinus rufipes), European elm bark beetle (Scolytus multistriatus), and the banded elm bark beetle (S. schevyrewi)). The beetles carry the DED fungal spores from tree to tree on and in their bodies. As the beetles feed on the elm tree, they create wounds through which the fungal spores can enter the tree. If neighboring elm trees have shared root grafts with an infected elm, the neighboring elm can become infected by movement of the fungus to the root system.

DED grows in the tree’s water uptake tissues (xylem) and ultimately blocks the tree’s ability to move water and nutrients. As the infected tree attempts to move water and nutrients from its roots, spores of the fungus are carried along and spread throughout the tree. As more of the tissues are blocked, the tree is not getting what it needs to survive and will die as a result. 

Signs and Symptoms

Dutch Elm Disease is a fast-moving disease; symptoms become apparent just 4-5 weeks after infection. The first sign that an elm may be infected is called “flagging”: leaves on one or more branches in the outer crown of the tree turn yellow, wilt and then brown before falling off. The infection then rapidly appears throughout the crown, as more leaves and branches die. Brown streaking can also be observed under the bark in the uptake tissues. 

Flagging symptoms can occur anytime during the growing season, but are usually observed in late spring or early summer. Out of season leaf drop is a good indication that the tree may be infected.

The rate of spread through the tree depends on the individual susceptibility of the tree. Infected trees can die the same season they become infected or over a period of several years. American elms, for example, are much more susceptible and often die within a single year after infection.

How does Teacher’s Tree Service manage DED?

Though Dutch Elm Disease is fast-moving, steps can be taken to manage and prevent the spread of the disease, including: 

Sanitation

Dead and dying elm trees should be removed and disposed of as soon as possible to eliminate them as a fungal source. Diseased branches should be pruned out of the tree before the infection has moved to the main stem of the tree.  Teacher’s Tree Service will properly prune or remove and dispose of your dead or dying elm.

Removal of beetle breeding sites

Don’t leave elm wood piled around the yard. Elm beetles overwinter and breed in piles of elm wood. Be sure to burn any elm firewood you have before beetles emerge in the spring.

Prevent root-based transfer

If neighboring elms share root grafts, we can excavate the roots and prune out the grafts to prevent spread from an infected tree to an unaffected tree.

Plant for resistance

If choosing an elm tree to plant on your property, be sure to choose a DED resistant cultivar. Don’t know which to choose?  Ask us! We can help you choose the right tree for your space and help you plant it.

Preventative fungicide injections

We can protect your healthy elm tree against DED by injecting it once every three years with a systemic fungicide. Contact us to see if your tree is a candidate for this preventative treatment.