Oak Wilt
by Anne Brown, HCMG |
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Oak wilt, one of the
most destructive tree
diseases in the United
States, is caused by a
fungus, Ceratocystis
fagacearum. This fungus
invades and disables the
water conducting system
of oak trees and greatly
reduces the flow of
water up the stem of the
tree. |
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Oak wilt was first
identified in 1944 and
is not unique to any one
region or state. The
disease is thought to
have started in the
eastern part of the
United States and has
been diagnosed in some
twenty states, and,
fortunately, has not
been identified in other
countries. All species
of oaks are thought to
be susceptible to oak
wilt in some degree, but
red oaks — particularly
Spanish oak, Texas red
oak, shumard oak, and
blackjack oak — are
extremely susceptible.
White oaks — post oak,
bur oak and Chinkapin
oak — have proven
resistant to the fungus.
Live oaks are
intermediate in
susceptibility, but can
be seriously affected
because of their network
of interconnected root
systems which allows the
fungus to move among
adjacent trees. |
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The mortality rate
varies among the
different kinds of oaks.
Red oaks die very
quickly from the
disease, usually within
three to four weeks of
symptoms appearing. Live
oaks die after one to
six months of symptoms
appearing. Approximately
10 percent of live oaks
may survive for several
years in various states
of decline. If oak wilt
is suspected, samples
should be sent to Texas
A&M for diagnosis by
laboratory analysis
there. |
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Control of oak wilt is
aided by several
approaches. Prevention
of new infections by
eliminating diseased red
oaks is of greatest
importance. Affected red
oat trees should be cut
down and burned. Pruning
properly and at the
right time is critical.
Never prune trees in the
spring –extremely cold
or hot weather is best,
and always paint the
wound immediately.
Trenching to disrupt
root connections can
help stop spread of the
fungus. Injecting
appropriate trees with a
fungicide can prevent
the tree from becoming
affected. The best and
most effective approach,
sadly, is planting trees
which are not
susceptible to the
fungus. |
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Oak wilt damaged limbs
or logs can be used for
firewood, with some
appropriate cautions.
Red oak wood should be
covered in plastic and
allowed to sit for one
year. If you purchase
firewood, do not
purchase red oak. Live
oak wood is all right to
purchase and burn. The
difference between the
two is red oaks form
fungal mats under the
bark, which can and do
easily spread. Live oaks
transmit the disease in
their roots and
therefore the wood is
safe to burn. |
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