Emerald ash borer threatens local tree populations

During a summer in the early 1990s, a freighter laden with shipments from northeast Asia pulls into port in Detroit, Michigan. The port authority, which oversees over 17 million tons of cargo per year, has just received a shipment it did not expect — a stowaway, hidden within the thousands of pallets and wooden crates.

Over the next 20 years, this miniscule immigrant would grow to become one of the largest threats to the health of eastern American forests, causing billions of dollars a year in damage control for local governments, and threatening the ruin of a keystone species of tree.

The emerald ash borer had made its way to America.

The EAB is a half-inch-long, metallic green beetle native to the forests of eastern Russia, northern China, Japan and Korea. According to the EAB Information Network, evidence of the insect wasn’t discovered in the U.S. until 2002 when populations of ash trees were found to be dying in southeastern Michigan. Research suggests that the beetle had established itself in the area 10 to 12 years before that, but had remained undetected.

Since its establishment, the EAB has spread outward from Detroit as far west as Colorado, south to Georgia, and north into Quebec and Ontario. According to the EAB Information Network, 23 states now have confirmed infestation sites, including New York.

“We have infestations in Niagara County, Erie County, Chautauqua County and Cattaraugus County,” said Patrick Marren, senior forester for the New York Department of Environmental Conservation. “The largest of those is in Erie County around Amherst, up by Buffalo. The Cattaraugus County infestation is the Randolph site which was the first one found in the state back in 2009.”

The ash borer causes damage during its juvenile stages as the larvae eats away at the sensitive inner layers of the tree, creating a distinctive s-shaped trail underneath the bark. This activity disrupts the tree’s ability to intake nutrients and eventually leads to its death in three to five years.

There are 16 types of ash trees in the United States, all of which appear to be susceptible to the beetles’ attacks. According to a 2011 document prepared by the Cornell Cooperative Extension, New York has around 900 million ash trees; meaning one in every 10 trees in the state is an ash. However, unlike Michigan and Ohio, where tens of millions of trees have already been wiped out, New York’s infestation levels are still relatively low.

“All of the ash trees in the state are at risk for being attacked and killed,” Marren said. “However, according to our best estimates under five percent of our forests are infested right now.”

According to Marren, one of the main accelerants of EAB distribution is the movement of firewood infested with the pest. As a response, the New York DEC issued a quarantine in 2009 making it illegal to transport wood, timber and ash products more than 50 miles from their source.

Sharon Bachman works as an educator for the Cornell Cooperative Extension’s Western New York emerald ash borer task force. The task force works to educate and help coordinate management plans for the spread of EAB in surrounding communities. Part of her job is to teach civilians why volunteer work and participation in mitigation efforts like quarantines are necessary for forest health.

“In terms of things like firewood movement,” Bachman said, “I think we really need to drive home the fact that this is something people need to be aware of, and they need to have an understanding of why they’re doing it and how it applies to them.”

Bachman said a population of ash borers will move about five miles per year without the aid of transported firewood. This relatively slow speed of distribution gives communities with ample amounts of time to prepare management plans for their own ash tree populations. While some experts are under the impression that the demise of the American ash is inevitable, Bachman maintains hope for three methods of control being utilized in New York.

The first method has exhibited impressive results in places like public parks where a definitive population of ash trees can be identified and monitored. It is an insecticide, Emamectin benzoate, which is sold under the name of Tree-age (pronounced triage). The poison is injected into the trunks of one-third of an ash population every year, so that after three years all of the trees have been vaccinated against the EAB threat. However, this treatment method is not applicable in larger areas such as forests.

The other two methods are the use of predators to the beetle, and selectively breeding resistant subspecies of ash, similar to those found in the beetle’s native Asian habitat. However, conclusive data on the effectiveness of these methods is not currently available.

Marren and Bachman agree that early detection and proactive management on the part of the public play a major role in defending against EAB infestation.

“It’s very important that we get all the help we can,” Marren said. “The more eyes out there searching for this bug gives us better chances of finding it early and slowing it down, so we have more time to educate local officials about this threat and help them with their plans.”

Observable signs of an infestation are things like thinning canopy density, increased woodpecker activity in the winter, vertical cracking in the bark, and v-shaped exit holes that matured beetles crawl out of during the summer. Anyone who thinks they might have an infested population should contact the New York EAB hotline at 866-640-0652.