Attention ash-tree owners: The day of
reckoning is here. An imported wood-boring bug called the emerald ash borer has
been wiping out ash trees over the eastern half of the United States, and it's
now fully parked in Pennsylvania. The bug is poised to kill just about all of
the 308 million ash trees in our forests, parks and neighborhoods.
"Our part of the state is
definitely in the eye of the storm," says Dan Devlin, director of the
state Department of Conservation and Natural Resources' Bureau of Forestry.
"It's impacting us quite a bit. Drive around, and you'll see dead ash
trees everywhere."
The borer's deadly work became
painfully apparent here last summer and fall. Chainsaws were buzzing overtime,
cutting down dead and mortally wounded ash trees in yards throughout the
Harrisburg area. Jackie Kauffman lost two mature ones in her New Cumberland
yard last September. "It's a real bummer, but we had no choice," she
said, adding that neighbors on her street have cut down six others.
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| Ash trees with bark damage from woodpeckers |
"Our Forest Hills neighborhood
(near Linglestown) has been devastated by the emerald ash borer," says Dan
Berman, a resident there. "I can drive down the streets and keenly point
out ash trees that are just a season or two away from meeting the tree-trimming
service."
The alarming part is that the emerald
ash borer is so devastating that it's expected to kill nearly 100 percent of
ash trees within four to five years. In other words, if you have one, it's
almost a sure bet to die - unless you take action to protect it with regular
applications of a chemical insecticides.
The emerald ash borer is an Asian
native that likely rode wooden packing materials to America. It was first
discovered destroying ash trees in Michigan in 2002. Since then, it's moved
mostly south and east by firewood and flight, killing tens of millions of all
species of ash trees in 20 states. The first ones showed up in central
Pennsylvania in 2012.
"It didn't take long to get from
Michigan to here," says Devlin. "It takes four to five years to kill
a tree. So by the time you see damage, the borer has been there several years.
It jumped ahead of everybody." As spring unfolds, we're about to see this bug's
peak performance.
Many municipalities, power companies
and tree-owners already are cutting down ashes pre-emptively. It's too
expensive to chemically protect masses of ash trees, and if you wait until
they're failing, they became fall hazards and much more expensive to remove.
(Brittle dead and dying ash trees are more hazardous for tree companies to work
on than healthy, solid ones.)
Ash-bearing homeowners face a similar
dilemma. Do you ignore the coming threat, figuring you'll pay later if necessary
while hoping the tree doesn't fall down in the meantime? Do you bite the bullet
and pay a few hundred dollars now to remove a tree that might look fine? Or do
you invest hundreds or even thousands of dollars for unknown years of
treatments to save your ash from the borers?
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| D-shaped exit hole |
The most effective treatment is an
insecticide called emamectin benzoate, which tree companies can inject into the
trunk of ash trees every two years. Michael Dunn, an arborist for Bartlett
Experts, says it's about 99 percent effective and is best applied in May or
June. Imidacloprid is a less expensive and more readily available insecticide
that homeowners can apply as a soil drench. But Dunn says it's only about 50
percent effective and has to be applied each year.
The key is that you can't wait until
the tree is badly infested. Signs of trouble include dieback of branches; bark
that turns light-colored ("blonding") and then starts splitting or
sloughing off; a rush of new shoots sprouting from the trunk, and woodpeckers
poking holes in an attempt to feast on the larvae inside. The telltale sign is
D-shaped holes in the trunk and large branches. Those are holes made in May to
early June by the newly matured adults exiting the tree to fly around and mate
in summer.
Adults look like elongated beetles -
less than the size of a small paperclip - with shiny, dark-green shells,, hence
the "emerald" in the bug's nickname.
After mating, females lay eggs in
bark cracks. The eggs hatch into larvae that look like fat, cream-colored,
worm-like critters (larva) that feed on the wood inside, ruining the trees'
ability to move water and nutrients up and down the phloem layer.
"Once a tree has emerald ash
borers, the treatment recovery rate goes down exponentially," says Dunn. Adds
Devlin: "People think they're catching it early when they're really not.
If the tree is looking bad, it's probably hopeless already." He says
chemical controls are more of an option for homeowners who have just one or a
few trees that they don't want to lose. The decision boils down to how valuable
the trees are and whether you're willing to spend the money to protect them.
"My recommendation is to get
somebody in there who's an experienced professional," says Devlin.
"One problem is that ash is brittle and breaks easily once it starts to
fail... The rule of thumb is that if there's an infestation within 10 miles,
and you don't have the borer yet, you might have a year before it shows
up."
Some say you may not have to treat
forever. If the borers move through like a tsunami wave and wipes out most ash
trees, their populations could crash in 15 to 20 years when there aren't
any/many ash trees left to eat. Others fear there will be enough floating
around to always be a threat - or worse yet, that the bug will adapt to other
species, such as related plants in the olive family. (The fringe tree is one
example where a few emerald ash borers already have been found.)
Still others are putting their hope
in the few ash trees - called "lingering ash" - that have managed to
survive in the borers' wake. Penn State University, for example, has lost 95
percent of the ash trees that forest biologist Dr. Kim Steiner planted in a
2,100-tree experimental green-ash grove in 1975. Most of the rest are expected
to die this year. "But we have about 15 trees remaining that show little
to no dieback," says Steiner, now director of the Penn State Arboretum.
Those and others in Ohio are being
studied for their borer-resistance with the hope that their genetics could be
the base for a rejuvenated after-life. Ironically, ash was widely planted as a
shady substitute for elm trees, which were nearly wiped off our botanical map
due to the deadly Dutch elm disease in the 1960s. Disease-resistant elm trees
are now being brought back after decades of back-crossing in which
"lingering elms" played a key role. The poetic justice is that these
new elms may now step back in as one of the possible replacements for ash.
For more information on emerald ash borer from Penn State Extension click here.
Reprinted from Penn Live
April 27, 2017
By George
Weigel
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