Dutch Elm Disease Management

Dutch Elm Disease

Dutch elm disease (DED) is an incurable and deadly fungal disease of elm trees. The fungal spores enter the tree, clogging the vessels that transport water and nutrients up and down the tree. This usually kills the tree in 3 - 5 years.

Click here for detailed facts about Dutch Elm Disease.

Click here to view pictorial information about DED

Trees

How is DED spread?

Dutch elm disease can spread by elm bark beetles or through root grafts and human activity.

  1. Elm bark beetles are small, shiny brownish-red beetles that are rarely visible to humans. Their activities, (egg laying, larvae feeding and overwintering), cause wounds in the elm trees. These wounds and the elm bark beetles themselves, release chemicals that attract more beetles to the elm trees. Elm trees can also have other wounds, such as pruning cuts or storm damage, which causes the tree to release a chemical that attracts the beetles. The beetles become covered with fungal spores from infected elm trees, which they spread to healthy trees as they move from tree to tree.
  2. There are a number of human activities that can spread Dutch elm disease such as: moving or storing infected elm wood; pruning infected/healthy elms without cleaning pruning tools between cuts; pruning elms when elm bark beetles are active (beetles hibernate during the winter); not removing DED infected elms; and improper disposal of DED infected wood (such as firewood).
  3. Tree roots from adjacent trees can connect and form grafts that allow nutrients and water to move back and forth from tree to tree. Fungal spores can be passed from tree to tree as well.
DED Spread
Larval feeding under tree bark causes fern like wounds unique to elm bark beetles.

DED in Charlottetown

DED was first recorded on PEI in the late 1970's. Charlottetown has been dealing with DED since 1996 through its tree maintenance program.

Charlottetown is not unique in its dealings with Dutch elm disease. Many municipalities across Canada from Manitoba to the Maritimes, have been struggling to manage this disease with varying degrees of success.

All of the native elms are susceptible to Dutch elm disease and, once they are infected, there is no known cure.

The Province conducted a partial survey of City owned elm trees in the summer of 2014 and the City followed with a complete survey of all elms on the public right-of-way.

           
Total number of Elms on City right-of-way 200 100%
Healthy Elms 73 36.5%
Elms Infected with DED 111 55.5%
Dead Elms 16 8%

 

Trees with DED
Drooping, wilting, curling, yellowing or browning of the leaves at the ends of the branches (called flagging) is one symptom of DED.
Photo by Andrew Williams.

It was found that more than half of the City owned elm trees were infected with DED.

Healthy Trees Infected Tress Dead Trees
2009
2013
2014

The City of Charlottetown also conducted a survey of the private elms in 2014. Below is a table displaying the complete results of that private and public elm survey: 


Healthy Diseased Dead Total
Public Land 73 111 16 200
Private Land 187 132 64 383
Total 260 243 80 583

The infected trees could not be saved. Many of these elms were located along streets, sidewalks and in our parks where there is high pedestrian or vehicle traffic. They were also located close to residential housing and businesses. The dead elms start to decay, exhibit poor structure and can become a hazard in the urban landscape.

DED, if not controlled, can quickly spread to our remaining healthy elm trees creating hazards and resulting in the loss of some of the City's largest and most beautiful trees.

Dutch Elm Disease Management

DED Management

As in some other municipalities, Charlottetown was seeing a significant increase in the number of DED infected trees due to stressors such as:

  • Weather events, such as drought and severe storms.
  • Milder winters that result in low bark beetle mortality.
  • The presence of a greater number of DED infected elms in the City.
  • Storage of elm wood for firewood, etc.

Unfortunately, past efforts had not stopped the spread of the disease. By applying proper management practices, it is possible to save some of the remaining elms. These elms provide numerous economic, social and environmental benefits to the city and its people.

The City consulted with other municipalities and carried out extensive research which gave the City the needed information and tools to manage DED.  Key components of a successful management program include monitoring, sanitation, tree planting, communication, education and community engagement.

What Does This Mean For Privately Owned Elm Trees?

To implement a management program for DED, it is important that privately owned elm trees are monitored and diseased trees removed. If infected trees (public or private) are left in the urban forest, they will continue to spread DED, making attempts to save the healthy elm trees futile.

The City takes responsibility for all elm management on both public and private land. Here's what you need to know if you have elm trees on your property:

  • Over the years, numerous elm trees have been identified as dead or diseased;
  • All DED infected and dead elm trees will be removed, including those on private property. This work will be paid for by the City;
  • You will be contacted by the City of Charlottetown if you have any elm trees on your property that are dead or diseased;
  • Elm wood must be disposed of properly.  If you have an elm tree removed due to DED, the City will remove all of the elm wood and dispose of it properly.  No elm wood is allowed to be stored and used as firewood;
  • You will be informed in advance if a dead or diseased elm tree must be removed from your property.
  • Stump grinding will be completed for every elm removed. Any property damage will be reinstated.

What Does This Mean For Elm Trees on Public Property?

Tree infected

The City is taking responsibility for all elm management on both public and private land. Here's what you need to know about elm trees on public property:

  • All DED infected and dead elm trees will be removed (public and private property);
  • The City of Charlottetown does its best to notify the owners of properties in close proximity to a publicly owned elm tree that is being removed;
  • Monitoring programs have been in place since 2014 that identify DED symptoms and watch healthy elms that may be at risk of being infected;
  • Stump grinding is completed for every elm removed. Any property damage will be reinstated.
  • The City plants trees on public property to help replace the elms that are lost to DED;
  • The City squares lost a significant number of elm trees to DED. Fortunately, there are many other species of trees in our squares that will remain;
Positive steps have been taken to replace some of the elms the City has lost to Dutch elm disease. The City has been planting DED resistant elm cultivars and hybrids since 2010.  Also, a  wide variety of other trees species have been planted throughout the City right-of-ways and parks, which increases the biodiversity of our trees and makes the urban forest less susceptible to insects pests and diseases.

From 2010 to 2014, about 70 healthy elms were inoculated annually in an attempt to increase their resistance to DED.  In 2015, The City switched to treating the healthy elm trees with a macro infusion system that included pumping a fungicide into the tree. This treatment last three years, so allows the City to treat healthy elm trees on a rotational basis. 

Reducing the Spread of DED

Keeping your elms healthy by providing water and fertilizer when needed and carrying out proper pruning makes your tree less stressed and more resistant to insect and disease pests.

  • If you have a healthy elm tree that you would like to protect, you can hire an arborist to treat your tree to increase its resistance to DED.
  • Regular monitoring of your elm trees helps to detect DED symptoms when they first appear.
  • Pruning may extend the life of your elm tree but will not save it once it is infected. There is no known cure for DED. To prevent the spread of DED, the best management strategy is to remove the infected tree.
  • Elm species should NOT be pruned between April 1 and September 30 as these open wounds attract the elm bark beetles which spread DED.
  • Timely removal and disposal of infected trees: Once DED is detected in a tree, the tree should be removed that fall/winter season, after the elm bark beetles are hibernating (after September 30). When an elm is removed, the stump should be ground and wood debris cleaned up.
  • Proper disposal is important. All elm wood should be disposed of by March 31. Any elms that must be removed during the summer months (i.e. for safety reasons) must be immediately burned or buried. When transporting the wood at this time of year, it should be taken directly from the location of removal to the point of disposal.
  • When planting trees, choose other resistant species or plant DED resistant cultivars of elm such as: Patriot, Pioneer, Regal, Valley Forage, Princeton, New Horizon, etc.

One of the most important ways to prevent the spread of DED is to not store elm wood as firewood. Elm firewood provides a great habitat for the elm bark beetles to carry out their lifecycle. The more successful they are at reproducing, the more beetles are present, the more DED is spread to healthy elm trees.

The City has now had an intensive DED management program in place for 3 years.  As monitoring for DED takes place annually, more elms are found on private and public land.  We have recorded a total of 963 elms since 2014.  The City has completed 4 rounds of removals.   A total of 526 DED infected elms have been removed since 2015.

There is still approximately 45% of our elms left in Charlottetown!

Each year, as the removal program takes place, the contractor piles the elm wood in our Squares and along our streets for pickup by City staff.  The City does not release any of this elm wood to individual homeowners. Your co-operation will help reduce the amount of DED that is present in our urban forest.

Still have questions? Contact us at: 902-566-5548