CREJ - page 23

April 2016 — Property Management Quarterly —
Page 23
B
y now, many Colorado resi-
dents are familiar with the
name emerald ash borer,
more commonly known as
EAB. In fact, it now is con-
sidered one of the most destruc-
tive forest pests ever seen in North
America.
To date, it’s held responsible for
killing more than 50 million ash
trees in over 20 states across the
country. In the Denver metro area
alone, there are 1.45 million ash
trees at risk, as the pest shows no
signs of slowing down.
Currently EAB remains in Boulder
County. But many experts agree that
this destructive and unrelenting pest
will soon be migrating past Boul-
der’s city limits, possibly as early as
June. The EAB population is build-
ing rapidly in northern Boulder, and
hundreds of trees are dying from the
infestation. Many speculate that EAB
has traveled outside of Boulder, but
has yet to be detected.
The Denver Parks and Recreation
Forestry Division is rolling out a pub-
lic education campaign about EAB.
Officials now understand the sever-
ity of the situation and are being
proactive in educating the public
about the long-term effects.
Ash trees are found throughout
Denver in public parks, green spaces
and rights-of-way, in addition to res-
idential properties, said Rob Davis,
with the Denver City Forester, in a
recent local newspaper article. The
trees perform important functions,
including cooling the landscape and
mitigating air pollution and storm
water runoff. “It is critical we acti-
vate a public awareness campaign to
help stop the infes-
tation of emerald
ash borer in our
community,” he
said.
What does that
mean for property
managers? If you
have ash trees,
you need to plan
ahead. Waiting to
treat until after the
borer is discovered
on your property or
an adjacent prop-
erty is not a good
strategy.
Once the borers are found, it is
likely they’ve already been there for
two to three years, causing signifi-
cant, if not irreversible, damage. Fol-
lowing are some commonly asked
questions about treating and pro-
tecting against EAB.
How effective are insecticide treat-
ments against emerald ash borer?
Under experimental conditions,
most results indicate a 90 percent
or higher success rate. In practi-
cal applications, success rates for
insecticide treatments are at least
80 percent effective. The discrep-
ancy is due to the condition of the
tree. Trees treated early, and in good
vigor, have the highest success rate.
The insecticides used to combat
EAB are nearly all systemic. That
means the insecticide is placed in
the soil or injected directly into the
trunk of the tree. The insecticide is
taken up into the tree via the vascu-
lar system. EAB and other ash borers
feed in that vascular system. When
the insects have compromised the
vascular system, the insecticide is
not able to disperse evenly through-
out the tree.
In addition to treating for EAB,
trees should be pruned while follow-
ing other good horticultural prac-
tices emphasizing tree health.
Will I have to treat ash trees forever?
The answer is yes and no.
EAB infestations follow a definite
curve. For the first three years, EAB
goes undetected while it infests the
trees. During the next two to three
years, borer populations build. Dur-
ing this “cusp” period, preventive
treatments are recommended. For
the next 10 years, the borer goes
through an exponential growth
phase.
Treatments for EAB are essential.
The result for most of the treated
trees is they live, while nearly all the
untreated trees die. With few trees
left for EAB to infest, the populations
of EAB will decline rapidly. Research-
ers in the Midwest are looking at
this post-mortality phase. It looks
as if treatments may be scaled back
after this period.
If I treat my trees, what should I
expect?
If the trees are not treated,
they will die. This is a known fact.
But many wonder if a treated tree
will look the same. The answer is
maybe … and maybe not.
While the success rate for insec-
ticide treatment is very high, when
EAB becomes prolific, they will chal-
lenge the tree – or begin feeding
on the tree before the insecticide
controls them. Thus ash trees, even
when treated, will accumulate more
dead branches than normal and
have a more sparse appearance to
the tree canopy. When the EAB mor-
tality curve subsides, the ash should
return to its normal vigor.
Ash trees make up approximately
15 to 20 percent of Colorado’s urban
forest. It’s no longer a question of
if EAB will spread to the Denver
metro area but, rather, a question of
when.
s
Steven Geist
Senior consulting
arborist, Swingle
Lawn, Tree &
Landscape Care,
Denver
Photo courtesy Swingle
Once emerald ash borers are found, like on a leaf pictured above, it is likely they’ve
already been there for two to three years, causing significant, if not irreversible, damage.
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