A Die-off of 3-5% of Connecticut’s Forests within 5 years from Invasive Ash Borer

Emerald Ash Borer (Credit: Claire Rutledge)


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As of this spring, the emerald ash borer, an invasive beetle that attacks native ash trees, is present in every shoreline town in Connecticut. In less than five years, it is expected that all ash trees in the region will be dead.

“The population growth is an exponential growth, it always catches people off guard,” said Claire Rutledge, an associate agricultural scientist at the Connecticut Agricultural Experiment Station. “Somewhere in the next three to five years most of the ashes in Middlesex and New London County will be dead, the growth curve is about to spike.”

The ash borer, originally from northeastern China, Korea and parts of Russia, was first found in Connecticut in July 2012, but only appeared in southeastern Connecticut in 2016, when it was detected in East Lyme.

“The emerald ash borer is currently devastating all of the ash trees,” said Gail Reynolds, the Master Gardner coordinator for UConn Extension in Middlesex County. “Ash isn’t a major presence in our forests, at most 15 percent, but it is a consistent presence. All ashes will die except for landscape trees that are periodically treated with systemic pesticides to kill the insects.”

Emerald ash borers infestation (Credit: Claire Rutledge)

Ash trees in North America have no effective defenses against these boring insects, and even healthy trees are can be felled by when emerald ash borers arrive.

When combined with recent damage to the Connecticut’s oak trees by the gypsy moth, the cost to the state and municipalities could be staggering.

“We are talking about a scope of tens of millions of dollars for tree removal along state roadways alone,” said Kevin Nursick, spokesperson for the Connecticut Department of Transportation. “Some locations are worse than others. Eastern Connecticut seems to have taken a pretty big beating from the gypsy moth, and anywhere there is an ash tree around the state it will need removal.”

In 2018, the cost of tree removal increased by close to $4.5 million over the previous year, and that number is just supposed to keep increasing, Nursick said. “It could be a cost of $30 to $50 million for tree removal.”

Cities and towns will also need to be proactive in removal of dead and dying ash and oak trees in order to avoid trees falling on houses, power lines, roads or people.

“The biggest noticeable impact of the emerald ash borer is on the municipal budget,” Rutledge said. “When trees die they fall down and we don’t want them to fall down on people.”

Rather than simply allowing the trees to die, some towns and individuals have to begun treating ash trees with systemic pesticides.

“For a municipality it can make a lot of sense to do treatment rather than removal,” Rutledge said. “The cost of taking down trees is not nothing. Treating the trees that are in good shape right now will save canopy and the ecosystem services of those trees.”

Per tree it can cost up to $500 every year to treat with pesticides, Rutledge said.

“One of the things we can’t stress enough is that you need to have a plan because towns will sort of toddle along thinking it will be alright to take them down as they die, but then you have 700 trees to take down in one year which is a lot of money or a lot of liability,” Rutledge said. “It is important for towns to get out in front and think about it.”

Tackling ash die-off across the region

Where the soil is typically sandier streets are rarely lined with ash, however, and although ash trees make up 3 to 5 percent of the forest statewide, the numbers can be significantly lower for shoreline towns.

That doesn’t mean the problem is far from the minds of many town tree wardens in the area.

“I just finished marking three dead ash trees for removal this morning,” said Tom Degnan, the tree warden in Old Lyme. “The selectman’s office brought up the need for a plan and the finance committee has asked if we need to allocate any funds, but I think the current budget is sufficient.”

The current budget for tree removal in Old Lyme is $20,000 per year.

Essex Tree Warden August Pampel also said Essex would not be expanding their tree removal budget. Just as in Old Lyme, many of the trees that need removal fall within the jurisdiction of Eversource.

“We are asking Eversource to take down a lot of them,” Pampel said. “Once they get within ten feet of the telephone poles the town can’t do it, Eversource has to.”

Eversource and other utility companies have been steadily working to remove dead ash and oak trees all summer, so much so that a waiting list for contractors has developed.

“It is very hard right now to obtain private contractors to do tree work, utility companies are doing so much work there is nobody left to hire with the training or equipment,” Nursick said. “Utility companies have been doing really good work protecting above ground cable infrastructure that it is also helping our roadways and the towns as well.”

Prevention and Mitigation

The primary way wood boring invasive species like the emerald ash borer travel from place to place is in firewood. That’s likely how it first arrived in New Haven County.

Prevention in part requires leaving wood at home and buying firewood on-site.

“It’s going to take a cultural shift,” Rutledge said. “I think of it like seatbelts or smoking, it will happen, but it’s going to take time.”

Stopping the transport of untreated wood will prevent new infestations, but to grapple with the one already ravaging the state’s forests, the Connecticut Agricultural Experiment Station has begun releasing wasps which predate on the emerald ash borer.

“The pattern is the emerald ash borer will kill all the mature trees, then the population of beetles will crash because they’ve eaten themselves out of house and home,” Rutledge.

The idea of releasing three parasitoid wasps into the environment now, is that when this crash occurs the wasps have a foothold and can prevent another explosion of the emerald ash borer population.

A parasitoid wasp to be released as a biological control (Credit: Claire Rutledge)

“What we are hoping is that these wasps will establish in the environment, follow down the emerald ash borers when their population drops and cause enough decline to let the ash trees come back,” Rutledge said. “There won’t be as many ash as before because they will still be impacted, but we are hoping that because these wasps have many generations per year they can help give the ash a break.”

The releases of wasps began in 2013, just a year after emerald ash borers were first detected. This year releases were performed in Kent, Coventry and Lebanon.