Alexandria ash trees under assault

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Alexandria ash trees under assault
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By Erich Wagner (Stock photo)

City officials recently announced they have discovered the presence of the emerald ash borer, an invasive insect that is fatal to some trees, in Alexandria.

The emerald ash borer is a small green beetle native to eastern Asia that feeds on ash trees, burrowing through the trunks and cutting off the trees’ ability to send water and nutrients to upper branches.

Although federal officials have set up plant quarantine protocols to limit the spread of the insect in recent years, the emerald ash borer has been found throughout the mid-Atlantic, Northeast and Midwest regions of the U.S.

City arborist John Noelle said the insect has a track record of decimating ash tree populations and destroying the tree canopy.

“It’s a severe problem in the Midwest and in the Northeast,” he said. “The emerald ash borer has just devastated many areas that have ash trees. One of its features is it is very specific to ash and it’s very aggressive. [Whereas some invasive species only attack weak trees], it has attacked ash trees throughout its geographic range, as opposed to just in areas where the trees are a little bit weaker or a little less healthy.”

Noelle said after the recent return of the ash borer to Fairfax and Arlington counties, city officials set up traps to see if the insect had migrated to Alexandria this summer.

“Those counties are no longer even putting out tracks to determine anymore — they’re just confident it’s present, and they’re acting accordingly,” he said. “So we put up monitoring traps this year, and immediately found that the borer is there.”

The arrival of the emerald ash borer comes after a number of difficult years for the city’s ash tree population, further complicating matters.

“One of the other things we’re dealing with is the ash trees seem to be suffering a little bit already,” Noelle said. “We’re getting toward the southern end of their range and have had a number of difficult summers and droughts. So
many of the trees are in decline in any case, and once they’re weakened, they become more susceptible to the emerald ash borer and other borers.”

Noelle said it is hard to say just how much of the city’s tree canopy is made up of ash trees. His office is only in the second year of a five-year process to catalog the city’s trees along streets and public land.

“We’ve divided the city into 20 different sections, and each year over five years we’re doing four of those sections scattered throughout the city,” he said. “We’ll go into that data, see where the ash trees are and then make a decision on how and what we’re going to treat.”

But treatment of ash trees is a difficult matter, Noelle said. It takes time for the effects of a borer infestation — the slow death of the tree’s branches and leaves from the top down — and it can take anywhere from two to five years for an affected tree to die.

Plus, outside of removing a dying tree, treatments are expensive and of varying effectiveness.

“You can apply a chemical systematically into the tree, but it’s not particularly practical,” Noelle said. “It’s a method that requires the treatment of one tree at a time. It also becomes a question of determining whether a tree has been infested, and at what point can you control the insect and still have a tree that’s viable?”

There is no city money specifically budgeted toward protecting trees against the ash borer, and unlike during the gypsy moth infestation of the 1980s and 1990s, the state has not set up a funding stream for local governments.

“Even when the gypsy moth was here, we just participated in the state program, and never did insect applications ourselves — it’s not our policy to do that,” Noelle said. “So we’re kind of in new territory now. How do we go about treating an insect that can cause significant damage?”

So the city is using its current general tree maintenance budget to test chemical treatments of trees to see how effective they are. Noelle recommended that residents with ash trees on their property consider chemical treatment as well, if the plant is still viable.

“There is a chemical, imidacloprid. It’s a solution, and you can do a soil drench with it,” he said. “There’s also a process of injecting it directly into the tree, so the chemical will be taken up into the crown. Both seem to be effective, although the injection may be a little more effective, since it will probably get more to the point of the tree where you need it.”

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