‘The typical result is annihilation’; N.C. Forest Service tracks the eastern front of the emerald ash borer

by | Apr 22, 2024

Purple prism traps, covered in sticky solution, are heavily utilized across the state to trap and detect emerging EAB infestations. Photo by Lili Stapel, N.C. Forest Service.

Wayne Langston, forest health specialist with the N.C. Forest Service, points out galleries left behind by EAB on the inside of the bark of an ash tree. Photo by Lili Stapel, N.C. Forest Service.

Insects are a natural part of the forest ecosystem. They play a pivotal role in discarding weak and inferior trees, breaking down and recycling littler on the forest floor and act as a food source for birds and other animals. However, certain insects pose a serious threat to tree and forest health. When these invasive insects attack healthy, valuable trees, killing them or weakening them to a point where other insects and diseases can infiltrate, they are considered pests. Insects and diseases claim more timber each year than any other forest menace.

As a result, April has been declared Invasive Plant Pest and Disease Awareness Month (IPPDAM) by the U.S. Department of Agriculture as part of an effort to raise awareness surrounding the risks brought on by invasive pests, diseases and harmful weeds to America’s crops and forests. IPPDAM is a celebration that focuses on educating the public on the importance of preventing the spread of these pests. While the rest of the country observes IPPDAM for the duration of April, some of these creepy crawlers appear to be doing some celebrating of their own by popping up and wreaking havoc in new places.

N.C. Forest Service Forest Health staff monitor all forest health issues across North Carolina by conducting specially designed surveys for forest pests which pose unique risk or high hazard to our state’s forest resources. These surveys target forest pests that are currently present in North Carolina as well as exotic pests that are not currently found in the state, but whose arrival could have catastrophic consequences. The N.C. Forest Service continually monitors forest health threats through aerial and ground surveys, permanent monitoring plots and communication and interaction with private landowners. One monitoring method carried out by the N.C. Forest Service is insect trapping.

Destructive insects such as the emerald ash borer (EAB), southern pine beetle (SPB), walnut twig beetle (WTB) and other exotic wood boring insects (EDRR) are trapped annually for the purpose of tracking their advance and monitoring population balances of invasive insects versus their natural predator. Each spring, forest health specialists with the N.C. Forest Service hike through forestland and wade through muddy swamps to strategically set traps for SPB and EAB.

An adult EAB recently extracted from an infested ash tree in the North Carolina Piedmont region. Photo by Lili Stapel, N.C. Forest Service.

EAB is a metallic green beetle that bores into ash trees and feeds on tissues beneath the bark, ultimately killing the tree. Native to Asia, EAB was first found in the U.S in 2002 when it was detected near Detroit, MI. A little more than a decade later, it trespassed into North Carolina for the first time when it was uncovered in Granville, Person, Vance and Warren counties. Since 2013, EAB has punctured and tunneled through ash trees in 72 counties as it has gradually spilled across the state, tracking east.

“The emerald ash borer is particularly concerning because it attacks and kills our native ash and white fringe trees,” said Jim Moeller, forest health specialist with the N.C. Forest Service. “Ash is a fairly important tree species both commercially and ecologically, and this insect is essentially removing it from our state’s landscape.”

Initial side effects of an EAB infestation include canopy dieback. Photo by Lili Stapel, N.C. Forest Service.

Wood from ash trees is valued for its strength and flexibility. It’s often used for products that require durability and resilience such as tool handles, baseball bats and bows. Ash foliage and seeds also serve as a food source for numerous animals as well as butterfly and moth caterpillars.

Adult borers lay eggs on the bark of ash trees. When the eggs hatch, the larvae burrow into the bark and begin feeding on the transportation tissues of the tree. This disrupts the movement of water and nutrients within the tree, ultimately beginning the strangulation process. Initial side effects include canopy dieback and epicormic branching or sprouting, which is when sprouting occurs from the main stem of the tree. These are indicators that the tree is under stress. Like most ailments, as the condition further deteriorates, the list of symptoms swells. Increased woodpecker activity, D-shaped exit holes where adult beetles have emerged from the trees, galleries on the inside of the bark and cream-colored larvae are also signs of an EAB ambush.

“While it may take anywhere between two to five years for a tree to succumb, the typical result is annihilation,” explained Moeller.

Treatment options are available for trees that are suffering from an EAB attack, although they are less than ideal. One remedy is through tree injections where the insecticide is absorbed and carried throughout the tree, but the cost for this type of treatment can be extreme. Another option is the soil drenching method when insecticides are mixed and poured at the base of the tree, where they are soaked up and ingested by the tree. Soil drenching is the cheaper option but it must be done annually and the larger the trees’ diameter, the less effective the treatment is.

Biocontrol methods have also been explored. Three species of stingless, parasitoid wasps have been released in many of the states where EAB has been found. The wasps attack either the egg or the larva of EAB, killing it. The biocontrol objective is to establish parasitoid wasp populations in areas infested with EAB to help manage EAB populations and reduce ash tree mortality. But, Moeller urges that the best defense against these bad bugs is through mitigation.

Jim Moeller, forest health specialist with the N.C. Forest Service, uses a hatchet to gently remove bark from an ash tree, exposing fresh galleries to remove the adult EAB. Photo by Lili Stapel, N.C. Forest Service.

“The biggest thing folks can do, and it’s also the easiest way to help reduce the spread of EAB, is to refrain from moving firewood.” Moeller continued, “It’s worth noting that this insect is one generation per year, meaning only one adult is coming out of the tree per year. While it can spread naturally by flying to new host trees, it’s only limited to a few miles per year.”

Simply put, this thing is getting a lot of help from humans by hitching frequent, long-distance rides across county and state lines by hanging out in untreated firewood. The spread of invasive insects in the state is often due to human activity through the transportation of infested wood products such as firewood. The first case of EAB in the U.S. previously mentioned in this article is believed to have been transported in wood packing materials made of ash. If the presence of EAB is detected early enough, dead and dying ash trees can be cut down, chipped or burned to reduce the chance of other trees suffering the same fate. Burn it where you buy it.

With EAB well encamped in roughly 75% of North Carolina counties, many wonder what the outlook is for the remaining undetected counties.

“It’s difficult to say when all 100 counties might be impacted, or which county will be the last one standing,” says Moeller. “Only time will tell as the insect’s movement progresses, but it seems imminent. We’re fairly certain we’re going to find it in more than one Eastern North Carolina county this spring.”