The Rural Voice, 2004-07, Page 51Woodlot Management
resistance, but without a vector of
spread, the disease may not have
been that significant. While it can be
spread between adjacent trees through
root grafts, the most common vector
of spread is by elm bark beetles.
As with many bark beetles, they
are attracted to stressed or dying trees
for brood sites to lay their eggs.
When young beetles emerge from the
dying trees, they travel to healthy
trees to feed. If their brood site was a
tree infected with DED. they are
likely to be carrying spores on their
bodies that can potentially infect
healthy trees. As more elm trees
became infected and stressed by the
disease, beetle populations also
increased due to the increase in
available brood material. no doubt
increasing the rate of spread.
Once most elms had been
eliminated in an area. beetle
populations likely collapsed and
incidence of the disease also became
very uncommon. No doubt many of
the young trees, that some viewed as
a comeback of elm. were likely
already established seedlings at the
time DED swept through the area, or
could have grown from seed
produced by large trees as they were
dying (stressed trees often produce
Targe distress crops of seed). As the
young trees have become larger in
recent years. beetle populations have
likely climbed, along with a
corresponding incidence of DED.
While we are currently seeing
many of our young elms succumbing
to the disease. a number of initiatives
are under way that may provide some
hope. It is surprising how many large
elms are still present across our
countryside. Perhaps these trees were
just missed by the disease, or poss-
ibly they may have some resistance.
A project currently beinglmdertaken
by the University of Guelph Arbore-
tum is attempting to see if they have
resistance. If resistance is found.
they plan to create a seed orchard of
resistant clones in hopes of breeding
resistant trees (http://www.uoguelph.ca/
arboretum/SpProjects/Elm_Recover 1
htm ). A number of other breeding
initiatives are underway, with some
nursery companies claiming to have
resistant cultivars.
In urban areas millions of dollars
are spent every year on protection
measures including pruning, injection
of systemic fungicide, fertilizing.
spraying to control beetles, etc. The
estimated value of a mature urban
elm for insurance purposes can
exceed $3,000, which certainly
justifies some investment in
protection. Recently a researcher
from University of Toronto has
developed a product that apparently
stimulates the trees natural defence
system to resist DED. This certainly
appears to have promise, but would
still have to be applied annually
(http://www.elmguard.com ).
Hopefully the elm will one day
recover, but even so. it is likely to
take generations. In the meantime.
landowners with large elms in their
woodlots or field boundaries should
try to retain them in hopes that they
may have some resistance to Dutch
Elm Disease and possibly pass the
resistance on to some of their
offspring.
If you have questions about
woodlot management or ideas for
topics you would like to see covered
in a future column. please contact
Steve Bowers at 519-482-3661 or
steve.bowers@mnr.gov.on.ca.0
Warren D. Moore
Forest Specialist
specializing in:
* Woodlot Management
* Timber Marking and Marketing
* Tree Pruning, Tree Removal
* Tree Planting Services
Certified Managed Forest Plan Approver
Provincial Tree Marker
Blyth 523-9855
A
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