'Pretty well infested': The emerald ash borer's destructive path

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Nine stumps. That's all that's left of a modest stand of white ash that once shaded a Pittsfield block.

Four years after the emerald ash borer was discovered in Dalton — the state's first known attack by the invasive species — the insect is ravaging Berkshire forests.

For ash trees, it looks like game over. That's already true for what might be called the nightmare on Cherry Street, after the city took down dead or dying ash on one block to protect the public from falling limbs.

"We're not going to be able to stop it," said Robert L. Presutti, of Pittsfield, a consulting arborist. "We're definitely not going to see ash trees for a long time."

Experts in forest health haven't given up entirely.

The state Department of Conservation and Recreation has been inoculating noteworthy ash trees on public land in a race to protect them. And in a counter-attack, DCR is releasing as biological control agents two types of wasps that feast on eggs or larvae of the emerald ash borer.

At the same time, environmentalists are watching other threats to New England forests, including the hemlock woolly adelgid and the Asian long-horned beetle — the bug responsible for a 2008 Worcester infestation that resulted in the removal of 31,000 trees.

But few believe the borer's advance can be checked.

"Pittsfield's pretty well infested," said Ken Gooch, forest health program director for the DCR. "It's spreading pretty fast here in Massachusetts."

Christian Mark, a floodplain forest ecologist with the Nature Conservancy, discovered the borer going after green ash in Longmeadow this fall after watching the invader move up the Connecticut River Valley.

"The emerald ash borer disperses really well. You only have to miss one," he said. "Slowing the spread hasn't seemed effective. It just keeps spreading."

PITTSFIELD IMPACT

Perhaps no one in Pittsfield knows that better than Tom Foody, street compliance inspector for the Department of Public Services. Foody quickly ran through his budget to deal with dead or dying ash trees on public rights of way, but plans more ash cutting next year.

"The budget was taxed because of the epidemic," Foody said of the infestation.

Foody has removed ash trees from streets around the city, including nine on Cherry Street just south of Tyler Street that were deemed hazards. He said almost all ash trees in Pittsfield appear to be affected.

"We knew they were coming," he said of the borers.

Curbing along the west side of Cherry between Lincoln and Burbank streets is now punctuated by stumps — with houses deprived of the previous tree canopy.

Gooch, the DCR's expert on forest health, said the borer infestation radiated out of Dalton after its discovery in 2012 on Pittsfield watershed land. The insects had probably been present for several years, having reached Massachusetts from what's believed to have been an initial infestation in Detroit in 2002. The borer is native to China and arrived inside shipping materials.

Since then, the borer has killed hundreds of millions of ash trees in 30 states. A study published this year in Ecological Applications estimated that the borer could cause $12.7 billion in damage by 2020.

What Gooch has seen since 2012 was predictable, given the insect's ability to fly for up to half a mile to extend its range. "Its instinct is to protect its species by dispersing widely," Gooch said.

The pest also hitches rides in ash cordwood transported for sale. Ash is popular as firewood because it is easy to split and cures quickly.

Though the borer is killing ash trees around the state, it has done the most damage so far in Berkshire County, according to Tawny Simisky, entomology specialist with the UMass Extension program at the University of Massachusetts Amherst.

That's in part because ash trees make up a high percentage of Berkshire forests, as well as being a popular urban tree. Before joined UMass, Simisky worked with Gooch at the DCR and helped run a trapping program used to track the advance of the borer.

Simisky recently updated a map of the borer's progress statewide. "Berkshire County has a larger block of towns highlighted that we know emerald ash borer is there, compared to other counties," she said. "Emerald ash borer is definitely the most significant threat to ash trees in Massachusetts and the United States."

A female borer lays eggs — 55 to 150 in a lifetime — in cracks on the bark of white, green or brown ash. When those eggs hatch, young larvae bore into the trees and feed on the cambium and phloem layers. That damages a tree's ability to circulate the nutrients and water it needs to survive.

The larvae leave telltale "galleries" — a hidden, meandering path of grooves in the wood layers.

By the time those galleries are found under bark at the base of trees, the insects have likely eaten their way down from the canopy, in multiple generations, dooming the tree.

After the pupa stage inside trees, the adults emerge, ready to take their appetites to another ash. When cutting through the bark to leave, they create distinctive D-shaped holes.

WASP ATTACK

Though trees can be inoculated against the borer, the cost is prohibitive. Gooch said it costs roughly $300 to protect a tree that measures 6 to 10 inches in diameter.

He has been working to save signature ash trees at one of the hardest-hit areas in Pittsfield, DCR's own headquarters at 740 South St.

"That place is just loaded," Gooch said. "Any ash tree that you drop, you can just peel the bark and find larvae."

A hundred dying ash trees have been taken down, but still others clearly in distress stand. They outnumber the few healthy ash. "Those are the only ones that have survived because I've treated them," Gooch said.

The infestation is so severe on the site that Gooch has brought Massachusetts College of Liberal Arts students there for a workshop.

Rather than inject trees with a chemical, the state's main strategy is to introduce an insect enemy.

Gooch has been introducing a type of wasp that deposits its eggs in larvae of the borer; when the wasps hatch, they feast on the target. Another type of wasp lays its eggs in the borer's eggs.

"The bottom line for us is getting biological controls out," Gooch said. "They are really good at going after the emerald ash borer but the borer has a bit of a head start."

Use of wasps to control the borer was subjected to federal studies before the technique was allowed to be adopted.

"Those species are well-suited to our climate and have been reproducing," Simisky, the UMass Extension entomologist, said of the wasps. Because they can expand their own numbers, the wasps don't have to be continually released. "We just need time for these biological control agents to build up and spread locally."

Presutti, the Pittsfield arborist, said the loss of ash trees will change the nature of the shade-tree canopy. He praises the ash as a "hardy" street tree that resists pollution.

"It's going to shift us to other species — it already has," he said. "Some along South Street [in Pittsfield] were appreciated for many years, but if they get diseased, they'll have to come down."

FUTURE HOPE

In the long term, preserving the ash may depend on finding trees that managed to survive — as certain Asian species have in China, the borer's home turf — and cultivating them.

Kate Birch, who volunteers to help plant trees in Pittsfield, said it may fall to science to keep ash trees in the mix.

"I'm hoping that scientists and botanists can find resistance for these," she said.

Marks, the Nature Conservancy ecologist, notes that efforts to bring back disease- or pest-resistant trees continue. But that work takes time because of a tree's long life cycle.

Projects to develop disease-resistant elm trees are only now coming to fruition, many decades after Dutch elm disease decimated that species. "A couple of decades is kind of a minimum, but maybe a century. It makes me hopeful about ash."

But that next chapter for the ash is, at best, a long way off.

"In the immediate future we're going to see a lot of trees dying," Marks said.

Reach staff writer Larry Parnass at 413-496-6214 or @larryparnass.


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