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Dutch
elm disease in Apple Valley
In an effort to maintain the vitality of
the community's urban forest, the City of Apple Valley has a Shade Tree
Disease Control Program to help control oak wilt and Dutch elm disease
throughout our community.
The City's Natural Resources Coordinator
is responsible for the coordination of the Shade Tree Disease Control
Program. The Natural Resources Coordinator is responsible for identifying
and controlling the spread of oak wilt and Dutch elm disease on public
and private property. A crucial component of this process is the identification,
communication, and coordination of shade tree disease control efforts
with the residents of Apple Valley.
What
is Dutch elm disease?
Minnesota's first case of Dutch elm disease
was detected in the Twin Cities in the early 1960s. Since that time, it
has been reported in all but a few of Minnesota's 87 counties. Link
to U of MN Extension Service Web Site for more information >>>
Dutch elm disease is caused by a fungus (Ophiostoma
ulmi) which invades and grows in the water conducting vessels of the tree.
The infected elm responds to the presence of the fungus and produces tyloses
and gums in the water conducting vessels in an attempt to compartmentalize
the fungus. By doing so, the tree prevents water from reaching its leaves.
Unfortunately, this attempt to stop the fungus is ineffective and ultimately
the leaves wilt and the tree dies.
The first signs of Dutch elm disease is apparent
due to the yellowing and wilting of the leaves in the upper canopy of
the tree. Eventually, the wilt will progress down the tree until all the
leaves have fallen off and the tree is dead. Depending on the amount of
water pressure in the water conducting vessels in the tree, it may take
the tree months to die. However, most trees will die in a relatively short
period of time.
How
Does Dutch Elm Disease Spread?
Elm
Bark Beetles
The Dutch elm disease fungus is spread
primarily by the European and the American elm bark beetles. The female
elm bark beetles lay their eggs under the bark of recently dead or dying
elm trees. As the beetles hatch out, they carry the sticky spores on
their bodies. They then fly to a live elm tree, bore into branches in
the upper canopy, and the germinating spore then enters the water conducting
vessels of this tree. This tree now becomes infected with Dutch elm
disease. After feeding, the female adult beetles breed and lay eggs,
producing yet another generation of beetles and repeating the cycle.
There are generally two to three generations of bark beetles per year.
Once an elm tree is infected, the disease can spread underground to
nearby healthy elms through grafted root systems.
Managing
the Spread of Dutch elm disease
Sanitation
A Dutch elm disease control
program will be successful only if organized on a city-wide basis with
the cooperation of property owners. The prompt removal and proper disposal
of all dead and dying elm wood is the single most important tool in
combating Dutch elm disease.
Proper sanitation is the
key in controlling the spread of Dutch elm disease. Annual inspections,
immediate removal of infected elms, and proper disposal of infected
wood, including firewood, are essential components for effective management
of this disease. If we can control the spread of the beetle and its
population, we can control the spread of the disease.
Proper sanitation requires that the diseased
elm tree is debarked, chipped or covered with a 4-mil poly making a
tight seal to the ground until all of the bark falls off. Once the bark
is no longer intact with the wood, it is no longer a nuisance.
Healthy elm trees which are removed and
kept for firewood will also provide bark beetle habitat. Therefore,
this wood also needs to be debarked, chipped or covered with a 4-mil
poly making a tight seal to the ground until all the bark falls off.
This will prevent the spread of the bark beetle.
Root
Graft Transmission and Disruption
Dutch elm disease also
spreads via root graft transmission. As roots grow, they intertwine,
they encapsulate one another causing an underground network of roots.
These root grafts allow the trees to compete for available water and
nutrients. Once an infected elm dies, it no longer has water pressure.
The next adjacent elm tree is able to pull available nutrients, water,
and the fungus into its system, thereby causing infection and spreading
the disease. Root graft transmission accounts for only 10 percent of
the spread of Dutch elm disease.
In order to stop the spread
via root graft transmission, the roots can be cut using a machine called
a vibratory plow which has a 5-foot blade. The root graft barrier isolates
the infected pocket of Dutch elm disease by severing the root graft
connection to the healthy trees. This in essence creates an island of
infection preventing the underground spread. Removal of the infected
elm tree will quicken the spread of the disease through the root system.
It is important that the root graft barrier be installed prior to the
removal of the infected elm tree.
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Figures 1 and 2: Root graft cutting
involves using a vibratory plow with a 5-foot blade
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Homeowners can hire a certified arborist
to inject their elm trees with a systemic fungicide in order to prevent
their trees from becoming infected with Dutch elm disease. The fungicides
can also potentially stop the spread of the disease within a tree that
is showing less than 10% crown wilt.
What
You Can Do
As a property owner, you can help control
the spread of Dutch elm disease by:
- Checking your neighborhood for dead or dying elm
trees, and
- Checking your woodpile for elm wood with intact
bark, and taking the necessary precautions to prevent further beetle
populations.
- If you suspect a problem, contact the Natural
Resources Coordinator at (952) 953-2460.
City
Regulations
City Ordinance 633, Section 20-55, Shade
Tree Disease Regulation declares diseased elms to be a nuisance which
negatively impacts the community. This Ordinance requires the removal
of all diseased elms and prevention of the spreading of the disease by
controlling bark beetle habitat.
A provision of this Ordinance allows for
City staff to inspect all properties on an annual basis in order to combat
the spread of Dutch elm disease.
For specific Ordinance information
or if you would like a copy of the Ordinance, please contact the City's
Natural Resources Coordinator
at (952) 953-2460.
Diagnoses
and Identification
The University of Minnesota
has a self-guided website to help homeowners diagnose their own tree,
shrub, vegetable, and turf-related diseases. Link
to the U of M Extension Service Site for information on Self Diagnosis
>>>
If you think your tree is
infected or your tree is diagnosed with Dutch elm disease, please contact
the Natural Resources Coordinator
at (952) 953-2460.
If the Natural Resources Department or Tree
Inspector identifies Dutch elm diseased trees on your property, the trees
will clearly mark and number them with yellow paint. A packet will be
sent which includes the following:
1. An official Notification Letter that explains:
a) Diseased tree removal procedures,
b) Assessment of the installation of a root graft barrier and/or the
use of a systemic fungicide.
2. A map showing the location of the infected trees
3. Oak
Wilt and Dutch Elm Disease Cost Share Program Policies 
4. A list of Licensed Tree Contractors
5. Dutch Elm Disease Cause and Prevention
brochure
Content updated on:
29-Aug-2008
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