Emerald ash borer decimating trees in WNC

STREET GAP, CHEROKEE NATIONAL FOREST - Paul Merten has spent nearly a decade chasing down a killer in the Southern Appalachians, armed with no more than a pocket knife and measuring tape.

But recently the entomologist with the U.S. Forest Service in Asheville has been homing in on the tiny, yet lethal pest with what he hopes is a secret weapon - parasitoids, also known as wasps.

Merten and Haywood County Community College forestry student Caroline McGough were deep in the woods on the Appalachian Trail slicing across the North Carolina-Tennessee border last week, unleashing parasitoids in a science fiction-like attack on the emerald ash borer.

The beetle is the latest in a series of invasive pests from Asia that are swiftly destroying ash trees across the country, causing billions in damage and wreaking havoc on biodiversity.

In a patch of ash trees in the rich cove forest, Merten released hundreds of the tiny wasps that feed only on the emerald ash borer in a “last Hail Mary” attempt to control the invasive insects.

The emerald ash borer, known as EAB, is a half-inch-long metallic green beetle first discovered near Detroit, Michigan, in 2002. It arrived from its native Asia, likely transported by solid wood packing material in cargo ships or airplanes, Merten said.

After arriving in Michigan, the beetle spread to the Midwest, having been found in Ohio in 2003 and northern Indiana in 2004. It continued its swirling path of destruction, arriving in New England in 2012.

The emerald ash borer made its first appearance in Western North Carolina in 2013 in the Great Smoky Mountains National Park.

The beetle was confirmed in July 2015 near the Tsali Recreation Area, on the south shore of Fontana Lake, in the Nantahala National Forest. Evidence of the beetle was also found on private land along the French Broad River from Tennessee to Marshall. The Animal and Plant Health Inspection Service has issued an ash quarantine for all counties in North Carolina.

The news is "devastating," Merten said.

“I’ve been chasing this insect for eight years. Emerald ash borer is a very fit species for what it does. It seems to locate its host species with great skill. It will probably generally infest North Carolina in the next couple of years,” he said.

Pre-emptive strikes

Emerald ash borer damage is actually caused by the larvae.

The beetles lay their eggs in between layers of an ash tree's bark. Larvae hatch in about a week and bore into the tree, feeding on the inner bark and phloem, the vascular tissue that transports nutrients to branches and leaves.

Their feeding creates “S” shaped tunnels, known as galleries. The larvae go through four feeding stages, which cuts off water supply and the flow of nutrients within the tree. They then go through the pupal stage in late spring. Adults begin to emerge in “D” shaped holes in May and June. The adults then go on to mate and feed on ash tree leaves, Merten said.

“They are exceedingly difficult to control,” Merten said. “They’re protected under the bark they’re eating. The window of opportunity to save ash trees is very short. They don’t have the vascular health to uptake the chemicals very well once they are infected.”

“We’ve been keeping a pretty good eye on ash trees,” said Kristine Johnson, supervisory forester with the Great Smoky Mountains National Park, where the beetles were first spotted on the Tennessee side of the half-million-acre park. “We haven’t seen mortality on North Carolina side yet.”

The Smokies are trying to get ahead of the EAB infestation by treating trees not yet infected, mostly in the Deep Creek and Chimneys picnic areas.

Using “Barney traps,” large purple traps that hang in ash trees with a scent believed to attract EABs, they hope to catch the beetles. If they find the insects, they use a systemic insecticide that is injected near the bottom of the tree trunk.

“Treatment is more effective when the tree is healthy, a pre-emptive treatment,” Johnson said.

It was more cost-effective to use a chemical treatment than to cut down dead trees, she said. The cost of the chemical emamectin benzoate is $1.25 per inch, while felling and leaving an infected tree would be $171.54 per 15-inch diameter tree.

The Smokies are using a $5,000 grant from the nonprofit Friends of the Smokies for the chemical treatment. They are now treating about 400 trees in the front- and backcountry.

The U.S. Forest Service is taking the wasp track.

Merten gets parasitoids, a natural enemy of the emerald ash borer native to Asia, from APHIS to use as a biocontrol. The female adult parasite wasp senses where the EAB larvae are, then pierces her ovipositor, a long tube that resembles a stinger, into the ash tree bark, Merten said.

The parasites lay eggs in and on the eggs and larvae of the EAB, which hatch and kill the beetle's eggs.

“It’s pretty crazy,” McGough said.

The two began releasing three species of parasitoids – oobius agrili, tetrastichus planipennis and spathius agrili – this summer in the Cherokee National Forest in Tennessee.

The forests in North Carolina did not choose to use biocontrol. But Merten said the wasps don’t read state lines, and is hopeful they will establish a population in North Carolina.

There are three ways of releasing them onto ash trees – as eggs in a small plastic cup attached known as an oobinator, as adults in jars and in small diameter ash bolts also infected with emerald ash borer larvae.

Deborah McCullough, professor of entomology and forestry at Michigan State University, said that in 2002, no one in the United States had studied the beetle before. Entomologists found two pages about the EAB in a Chinese textbook that had to be translated to English.

“We didn’t know the biology, we didn’t know if it would attack other trees. We didn’t know how to stop it,” she said. “We knew it was going to be a big deal, but no one anticipated the amount of destruction, the dead trees, the economic costs and the ecological impacts as well.”

At that time there were few systemic insecticides available, and the ones they tried had inconsistent results. The course of action was to cut down trees within a half-mile radius of infested trees because EAB can be present in an area before a tree starts to show damage, she said.

Now much better systemic insecticides, like the ones being used in the Smokies, are available.

However, they are mostly effective before a tree gets infested. She said insecticides should be used by landscapers and homeowners to preserve ash trees wherever emerald ash borer is known to exist.

McCullough said another measure is seed banking - saving ash seeds for research and for eventual replanting.

“To me it’s incredible that in 14 years we’ve gone from knowing EAB existed to freezing seeds in the hopes that we come up with something better to control. As of last week it is confirmed in 28 states and two Canadian provinces,” she said.

Demise costs billions

There are 16 species of ash in the United States. The emerald ash borer infects the white and green ash trees found in WNC. They do not affect mountain ash.

White ash tends to grow at higher elevations, in drier soils, while green ash likes moist soils along rivers and streams.

Considering that ash trees make up 3-5 percent of forested land in WNC, and how quickly the beetle moves, Merten said the trees could be wiped from the forest in a few years, much like the American chestnut disappeared from the landscape due to the chestnut blight in the mid-20th century.

The loss of ash trees is disturbing because of its splendor – they are canopy trees that can grow to more than 100 feet high, provide yellow to orange foliage in the fall, and are a backbone of landscaping. They are also an important source for lumber, furniture, firewood and paper, and are the preferred wood for baseball bats.

Green ash is important for riparian areas – it holds soil to prevent erosion, and provides shade for streams, keeping temperatures cool for fish and aquatic life.

Loss of the trees would also remove a carbon sink. These all-important forested areas remove carbon dioxide from the atmosphere, which is essential in slowing climate change.

“When ash trees die, we’re losing diversity, we’re losing part of the ecosystem,” Merten said.

A report by APHIS, the Agricultural Research Service and the U.S. Forest Service estimate federal and state resource managers spend $29 billion a year to manage EAB populations. They estimate the value of the 8 billion ash trees in the U.S. potentially infested with EAB to be $282 billion.

Human influence

The beetles are good at flying, but they are also unwittingly being helped by humans, Merten said. One of the biggest culprits is firewood. People cut up dead ash trees infested with emerald ash borer, then bring it on camping, hunting and fishing trips, releasing the beetles in new areas.

“Beetles can travel like a Trojan horse, undetected by anyone. They can arrive in a new place and voila, you have a new infestation,” Merten said.

He said people should only use locally bought firewood, and use heat-treated firewood, which is stamped with a USDA symbol.

A report released in May in the online journal Ecological Applications, says that imported forest pests, such as the balsam and hemlock woolly adelgid, gypsy moths, beech bark disease and emerald ash borer are the No. 1 threat to forests across the U.S.

“Unfortunately, I think we’re losing the battle with EAB,” Merten said. “But the next pest on the horizon is the Asian long-horned beetle, which has every opportunity to be as bad or worse than EAB.”

The Asian long-horned beetle, which kills a variety of trees, including maple, is now confirmed in New York, Massachusetts and Ohio. They are also largely thought to be transported by firewood.

“If we could get people to stop moving firewood we could slow the spread,” Merten said. “I think people fail to grasp the gravity of their actions.”

Learn more:

For more information on the emerald ash borer, including a bulletin describing the signs and symptoms of EAB and an insecticide fact sheet, visit www.emeraldashborer.info.

If you think you have EAB or EAB damage on your property, call your county Cooperative Extension office. Call the Buncombe County office in Asheville at 828-255-5522 or visit https://buncombe.ces.ncsu.edu/.

In North Carolina, you can also call 800-206-9333 or email newpest@ncagr.gov.

Tips for preventing the spread of emerald ash borer:

• Don't bring your own firewood to campgrounds or other forested areas.
• Obtain firewood from the forest in which you are camping or from a nearby vendor.
• If you have moved firewood, burn all of it before leaving your campsite.
• Only buy heat-treated firewood, labeled by the U.S. Department of Agriculture.

Source: U.S. Forest Service