what is dutch elm disease? (DED)

Dutch Elm Disease (DED) is a vascular disease which has killed countless planted and natural stands of native American or White elm trees, Ulmus americana L.

The Siberian elm, U. pumila L., an introduced tree, does not appear to be as susceptible to DED as the American elm.In fact, there has only been one confirmed case in Winnipeg of DED in a Siberian elm.

HISTORICAL DISTRIBUTION OF DUTCH ELM DISEASE IN NORTH AMERICA (1930 – 2000)

Dutch Elm Disease distribution in North America

Map Courtesy Sunday Oghiahke, University of Manitoba Entomology Department

history of DED

DED is the most destructive disease of elms in North America. It has devastated elm populations around the world. DED was first identified in the Netherlands and northern France in 1919.The disease was brought to Europe from the Dutch East Indies in Southeast Asia during the late 19th century.

The first infections in North America were observed in Ohio in 1930. In Canada, the disease was found in Richeleau County, Quebec in 1944. Since then, DED has spread to almost every area in both Canada and the U.S. where there are ranges of native and planted elms. DED entered Manitoba via the United States from diseased firewood that was transported across the border

Before the occurrence of DED in Manitoba, it is estimated that the natural elm population in the central and southern portions of the province was approximately 20 million trees. Also since the early 1900's over five million elms were planted in cities, towns and in rural shelter belts.

Although DED was rampant in eastern Canada, it was not until 1975 that the disease was found in Winnipeg. A handful of diseased elms were first sighted in Wildwood Park, a lovely enclave on the banks of the Red River. Municipal and provincial officials sprang into action and initiated a cost-shared, integrated program of control which currently includes surveillance, sanitation, pruning, removal, therapeutic injections, basal treatments, education, community action, research, reforestation and preventative programs.

In 1980, Manitoba enacted the Dutch Elm Disease Act, a legal framework for the administration of the DED control program.

By 1990, the DED program was a fully integrated pest management effort that encompassed 50 towns, cities and municipalities across an area of approximately 100,000 square kilometers.

Over the years, both the province and the city have spent a lot of money to manage DED losses. In Winnipeg, over $2 million each year is spent on DED control. The annual loss of elms to DED has been kept to a level of less than 2% of the total inventory.This figure is considered acceptable to maintain a large elm population. More recently the loss rate has crept up to 3%. We are currently working with the Province of Manitoba and City of Winnipeg to reassess the DED program and revise the management practices.

what are the symptoms of DED?

DED Fungal Hyphae clogging elm wood pores and cells

Please note that Tanglefoot© Bands are designed only for cankerworm control, and have not been scientifically proven to prevent Dutch elm disease. For simple tips on how to help prevent DED, please click here.

The symptoms of the disease first appear in the leaves and can be observed from June to mid-August.The first symptom is the sudden wilting or drooping of the leaves on one or more of the major branches in the crown of the tree.This stage is subtle and difficult to identify by the untrained observer. With experience, it becomes easier to pick out the earliest phase of DED

The next stage is termed flagging as the leaves first turn yellow, then brown and shrivel.

As the disease advances, and it can do so at a rapid rate, the affected branch or branches die and more of the tree becomes infected. Most discoloured leaves will fall from the tree although some will remain on the tree into winter.

If infected later in the summer, the leaves will turn yellow and droop. Premature leaf drop often occurs. These infections are difficult to distinguish from early fall colouration which can occur as early as mid-August.

Elms that are infected later in the season may not show any symptoms but will have smaller than normal leaves the next spring. The tree will suddenly wilt and die rapidly in early summer.

Symptoms of the disease can also be seen under the bark of infected branches. Dark brown streaks in wood can be seen by removing the bark. Occasionally, the elm is affected by other diseases such as Verticillium wilt and Dothiorella wilt, which can mimic the symptoms of DED If this is suspected, it may be necessary to test the sample in the laboratory to determine which disease is responsible for the symptoms.

what causes DED?

DED is caused by the fungus Ophiostoma ulmi which produces a toxic substance, to which the tree reacts, blocking the water conducting cells of the tree. The cells lose their normal function, resulting in wilting leaves and ultimately, the death of the tree.

DED is fatal to both large and small trees. The time it takes to kill the tree varies, depending upon age and growing conditions. Although younger trees seem to be somewhat less vulnerable than older trees, when a younger vigorous tree becomes infected, it can die within a few weeks. Older, slower growing trees may live for a year or two but eventually succumb to the disease.

how does DED spread?

DED is spread by elm bark beetles, primarily the Native Elm Bark Beetle. (The European Elm Bark Beetle also carries the disease but presently is not a concern in Manitoba.)

The tiny beetles (1/8 in. or 3 mm long), dark brown or black, carry the disease spores on their bodies from infected trees to healthy elms on which they feed.

The adult beetle breeds in recently dead or dying elm wood. Breeding takes place between the bark and the wood where the female constructs brood galleries (channels) in a V-shaped formation at right angles to the grain of the wood.

Eggs laid along the brood galleries hatch and the larvae feed, producing their own galleries. Whenfully developed, the larvae pupate and emerge as adults. If this breeding takes place in diseased wood, the new adult beetle may emerge with the very sticky DED spores attached. These spores can cause new infections if introduced into the water conducting tissues of healthy elm trees when the beetle feeds in the upper crown of the tree.

The life cycle of beetles varies: adults overwinter in the base of healthy elm trees. Larvae overwinter in brood trees and wood. The over wintering adults emerge in mid-April to mid-May and feed briefly before selecting brood material. This feeding stage is responsible for the majority of DED infections.

Signs of beetle activity can be seen in spring or fall as red boring dust on the lower trunk bark of healthy elms.

To a lesser extent, DED may be spread by underground root grafts between trees up to 40 feet or 13 meters apart.

DED management

Community Involvement
Legislation
Preventative Measures
Reforestation
Research

Community Action: The Elm Guard Program

As municipal resources decline, community action is essential in the fight to preserve the elms. Elm guard groups are active in many communities throughout Manitoba. These groups learn about the disease, how to detect DED and contact municipal officials to report suspected diseased or dying trees.

introduction - Community Action

The fight against DED is not a lost battle. In Manitoba we have shown that with sufficient government funding and commitment by the people, we can protect our mature elm populations. As well as educating ourselves about DED, especially learning about the signs of the disease and what to do about it, we should care for our elms to prevent the disease from occurring in the first place.

The greatest incidence of DED occurs on private property. In Winnipeg, it is estimated that over 80% of DED occurs in our yards. In rural areas, the problem is the same. Shelterbelts have been especially hard hit by DED Despite the greatest efforts of municipalities, DED management programs cannot prevent the destruction of private trees. Homeowners can and must do their part to protect their elms.

Many homeowners spend time and money on the flowers and grass in their yards. Trees are often left to fend for themselves. Dead wood on elm trees accumulates and becomes a breeding site for the elm bark beetle. DED then strikes and often spreads to public street elms resulting in greater losses of DED despite the effort of municipal DED management programs.

A common argument against taking care of our trees is that the cost is too great. It is true that it can be a fairly expensive proposition to prune mature trees. However, one must remember that the cost of pruning should be amortized over a number of years. Pruning is only required once every 7-10 years or as required from storm damage, for instance.

The cost of watering and fertilizing is minimal if done properly. Trees enhance property values and also reduce energy costs. Healthy trees are worth the investment.

Advantages Of An Elm Guard Group

By working with your neighbours in an elm guard group you can:

Obtain group rates (perhaps 10-20% reduction in costs) for pruning and tree care from tree service firms
Organize a basal spray program to control the elm bark beetle. (You provide authorization for the City to enter your property and the Forestry Branch will treat the base of your elms free of charge.) Get your neighbours involved too!
Attend workshops and learn how to care for the trees in your own backyard.
Plant trees at neighbourhood parks and playgrounds. (Make sure you obtain authorization from the appropriate local officials.) Information is available from the Coalition to Save the Elms and local officials on funding opportunities to purchase trees.
Band trees for cankerworm control on Labour Day. Make sure to remove the bands by the May long weekend.
Help preserve the character of your neighbourhood.
Get to know your neighbours and make new friends!

The Elm Guard Program: Roles and Responsibilities

Learn how to identify American elms, detect DED, identify hazard elms (more than 50% dead), and spot elm firewood.

Divide your neighbourhood or area into assigned territories. Survey your assigned area one to two times per week during the period of mid-June to mid-August. Don't forget back lanes, parks and riverbanks. During your surveys:

Look for the Symptoms of DED
If the tree shows signs of DED, loosely tie flagging tape (supplied by the Forestry Branch) around the trunk for identification, fully complete the "Elm Guard Request for Sample" form and immediately provide it to the elm guard coordinator who will convey the information to the Forestry Branch.
The Forestry Branch will then examine and if necessary, tag the tree for future identification. In Winnipeg, if the elm has DED or is deemed a hazard tree, it will be removed by the city. If you live in a rural area, check with your municipal office to see if your town has a DED management program and cost-shared arrangement with the province.
Check firewood piles for elm wood. Elm wood is distinguished by bark that is dark grey/brown in colour, has broad intersecting ridges and a rough flaky appearance. The bark cross-section has alternate brown and beige layers - a feature distinctive to elms.
If you see someone pruning an elm tree between April 1st and July 31st, report it to the city's Forestry Branch or the local Natural Resources officer. It is illegal to prune elms during this period as the fresh wounds are attractive to the elm bark beetle which spreads DED
If you are on holiday during the summer, please ensure that you have a back-up person or neighbour to patrol your assigned area.

For more information about the elm guard program please contact Trees Winnipeg at 832-7188, or the City of Winnipeg's Tree Line at 311 or the Manitoba Conservation official in your area. The Provincial Tree Line phone number in Winnipeg is 945-7866.

legislation

In 1980, the Dutch Elm Disease Act was proclaimed to prescribe programs and measures for the control of DED in Manitoba. The main features of the Act and Regulations include:

The prohibition of pruning American elm between April 1st and July 31st (when the elm bark beetle is actively seeking new breeding material)
The prohibition of stored elm wood.
The proper disposal of elm wood by burial, chipping or burning
The right of entry and inspection: appointment of inspectors with specific powers such as the right to enter properties to conduct inspections and carry out control procedures.
The requirement of possessing a Manitoba Arborist license when engaged in commercial activities relating to the care of elms.
Penalties for contravention of the Act: a maximum fine of $5,000.

For further reference, the Manitoba Dutch Elm Disease Act is available online here

preventative measures

Basal Treatment

NOTE

The City of Winnipeg has requested that the Coalition to Save the Elms stop taking individual basal spraying request applications from members of the public from this date forward. Over the last two years, the City has re-focused the program to spray trees along riverbank areas within the City of Winnipeg. Normally, these riverbank areas are where Dutch elm disease and the Elm bark beetle populations are the highest. It is believed that focusing limited resources in these areas is the most efficient and effective way to control Dutch elm disease in Winnipeg.

Furthermore, the City informs the Coalition that those registrations the Coalition to Save the Elms has collected in the past will receive the lowest priority for spraying. These registrations will be sprayed only if time and resources permit. The reasons for this change are as mentioned above.

Should residents have any questions about this change, please call The City’s Customer Service Center at 311.

As well as removing their breeding material, elm bark beetles can be controlled with insecticides. A registered insecticide containing the active ingredient chlorpyrifos is most effective in controlling overwintering beetles for up to 2 years.

Research has shown that chlorpyrifos breaks down quickly in sunlight while retaining its chemical effectiveness deep in the fissures of the bark. If applied properly, there should be little spray drift.The spray is applied to the lower 25 cm of the tree. The chemical will prevent adult beetles from overwintering in the tree and is applied every two years. Effectiveness also increases with the number of trees treated. The beetle population can be reduced by more than 98%.

In Winnipeg, the city sprays all boulevard and park elm trees to reduce the elm bark beetle population. You too, can have the the base of your elms in your own yard by registering in the Basal Spray Program with the Coalition to Save the Elms. The basal spray application is done from August to October by the City of Winnipeg.

In Winnipeg the City will apply the basal treatment, at no cost to the homeowner. The Coalition to Save the Elms volunteers work with the City obtaining signed authorization forms from homeowners allowing access to their property. Homeowners, living in close proximity to rivers where the disease is often concentrated, should take advantage of the opportunity to have their elms treated by the city. But for the treatment to be most effective it is helpful to spray as many elms as possible. Obtaining the support of your neighbours will be of great value for everyone.

In rural municipalities, elm trees are treated by the municipality only if that municipality participates in the DED Cost Sharing Agreement Program managed by Manitoba Conservation

elm tree sanitation

Sanitation is the removal of all identified diseased and hazard elm trees as soon as possible after detection. It also includes the removal or treatment of remaining stumps.

To prevent the spread of DED to healthy trees, it is essential to remove diseased, dying and dead elms. These trees are ideal breeding material for the elm bark beetle.

Elm firewood is a perfect breeding site for the beetle. It is also the perfect means of transporting DED from place to place. Detection and proper disposal of elmwood is especially important.

Fungicide Injections

American Elm therapeutic injection by perennial trees

The injection of fungicides into elm trees is another method of protection against DED The fungicide is injected into the vascular system of the tree circulating throughout the trunk, branches and crown.

The chemicals Alamo and Eertavas are currently registered for use in Canada.

There are two types of injection: root flare and trunk injection.

Root flare injection is more commonly used. Holes are drilled through the bark into the wood around the base of the tree. The injector heads are inserted into the holes and the chemical is injected. Injections can be done at any time of the growing season. For the greatest protection, injection should be done when trees are in full leaf before the end of June.

Which trees should be injected? As injection is an invasive, expensive and difficult preventative procedure, only healthy high-value elms should be treated.

However, injection may also cure trees in the early stages of infection. Treating diseased trees is not recommended unless there is less than 10% infection or crown wilt present. Extensive crown wilt indicates a well-established infection that will not respond to injection. Pruning of diseased branches should be done before or as soon as possible after the tree is injected.

The effects of the fungicide last perhaps two years. Injection is a costly procedure that does not provide a cure or long-lasting resistance to DED

surveillance

Wild American Elms marked for DED removal

Surveillance is a systematic survey of all the elms in the control area to detect both diseased and hazard (more than 40% dead) elms as well as stored elm firewood locations.

In Winnipeg, surveillance is the responsibility of the city's Forestry Branch. In most areas of the city, surveillance is carried out twice each summer. In 1996, the Forestry Branch instituted an enhanced DED control program which resulted in the weekly survey of some areas in the city. In rural communities participating in the cost-shared program, Manitoba Conservation carries out surveillance.

In Winnipeg, there are a number of elm guard groups who have been trained in the detection of DED and who assist the Forestry Branch by surveying trees in their neighbourhood.Communities such as Neepawa and Brandon also have active citizenry who keep an eye out for the signs of DED The information collected from the surveillance is then computerized and used by removal operations crews.

If you learn to spot the signs of DED in the very initial stages of the disease, and your elm is a mature high value tree, you can have it injected with a fungicide.

The use of elm as firewood is restricted by law in Manitoba. Unfortunately, many people do keep elm wood. The wood, unless debarked, is a habitat for the elm bark beetle. It is essential to recognize elm wood to help prevent the spread of DED

If the homeowner is storing elm wood in contravention of the Dutch Elm Disease Act, a notice will be left requiring the homeowner to properly dispose of the wood.

reforestation

In areas where DED is rampant, the selection and planting of alternate species of trees can be considered. species such as green ash, black ash, basswood or linden, silver maple, Schubert, chokecherry and common hackberry grow well in southern and central Manitoba climates.

However, the replanting of American elms is also recommended in areas where DED management programs are in place. No other tree can replace the majestic elm. While it is important to avoid planting a monoculture of tree species, it is equally important to the long-term survival of the elm that new growth be encouraged as well. Hopefully, research will find a long-term solution to DED in the near future.

research

Extensive research into the mechanisms of DED, the habits of the elm bark beetle and the existence of naturally occurring disease-resistant strains of elms is being carried out in Manitoba and Ontario. The Coalition to Save the Elms has been instrumental in encouraging multi-level government support of promising research at the Universities of Manitoba and Toronto. With the support of the Coalition and the public, research has been funded by the City of Winnipeg, the Province of Manitoba, and the federal government.

At the University of Manitoba, research is being conducted on "field-resistant" strains of elms. Thousands of American elm seedlings are being screened by Department of Plant Science and Manitoba Conservation. Although the research looks promising, it will take time before a DED-tolerant American elm is identified.

Additional research being proposed by the University of Manitoba in collaboration with Manitoba conservation and the City of Winnipeg will look at three areas of study:

Identifying more specific behavioural characteristics of the native elm bark beetle to better understand the transmission of DED fungus by the beetle,
Assessing alternative chemicals to Dursban or Chorpyrifos for basal spray treatments to control native elm bark beetle, and
Assessing the effectiveness of rapid removal of diseased elms.

Although the City of Winnipeg has the most successful DED management program in North America, progressive thinking in our urban forestry sector identifies that changes can be made to improve the program over the long term. This research is critical to sustaining a healthy urban forest and environment. There are still many unanswered questions about the behaviour of the native elm bark beetle and DED. Most other research in North America has traditionally focused on other species of beetle that are not prevalent here. This currently proposed research will provide the evidence needed to make more changes.

DUTCH ELM DISEASE (DED)