An invasive pest is killing North Carolina’s ash trees. Are your trees at risk?
An invasive pest is quickly making its way across North Carolina, and it’s wreaking havoc on the state’s ash trees.
The Emerald Ash Borer (EAB) first started ravaging the hardwood trees around the state in 2013, and in 2015 it was detected in Wake, Durham and Orange counties.
Today, the pest is present in at least 60 of the state’s 100 counties.
Jennifer Roach, district forester for the N.C. Forest Service district that includes Wake, Durham and Orange Counties, said county forestry offices generally receive between three to five calls per week about unhealthy or dying ash trees in the area.
We talked to Roach and to NC State professor and forest health extension specialist Kelly Oten about ash trees, and learned how to tell if ash trees in your yard are infested, what treatment options available and how to help prevent the spread of the EAB.
What are ash trees?
▪ Ash trees are large shade trees. They typically grow to be between 40 and 60 feet tall, and some varieties can reach 80 feet.
▪ Ash trees are hardwood trees. The wood harvested from ash trees is hard, dense, tough and strong, making it useful for making tool handles and baseball bats. It is also used in some furniture applications.
▪ Ash trees have opposite, pinnately compound leaves. This means a single ash tree leaf is made up of several smaller leaflets that originate from a single, slender stem. The leaves are paired on the stem, rising at the same node, or level, on opposite sides of the stem.
▪ Ash trees are deciduous. They generally shed their leaves in the fall, remain bare through the winter and produce leaves again in the spring.
Ash tree varieties in North Carolina
▪ Green ash trees are widespread across the state, growing mostly in low-growing woods and flood plains.
▪ White ash or American ash trees typically grow in rich upland or lowland forests. They are found throughout North Carolina, except near the coast.
▪ Carolina ash or water ash trees are found mostly in the low woods of eastern North Carolina.
▪ Pumpkin ash trees are commonly found in the swamps of eastern North Carolina.
Ash trees account for 2%, or about 250 million trees, of North Carolina’s natural forest, according to Oten. Local cities and counties often use them to line streets or other public spaces, such as parks, Oten said.
Fun fact: Despite their name, mountain ash trees are not ash trees.
If you need help identifying the trees in your yard, you can contact your N.C. Forest Service county ranger. You can find your county ranger at ncforestservice.gov/contacts.
What is the Emerald Ash Borer?
The Emerald Ash Borer (EAB) is an invasive, wood-boring beetle indigenous to China, Japan, Korea and parts of eastern Russia that preys on ash trees.
EABs were first discovered in the United States in Detroit, Michigan, in 2002. The pest was discovered in North Carolina in 2013, and has since spread to 60 counties.
Oten described the EAB as “one of the most quickly spreading invasive forest pests to ever invade North Carolina.”
Emerald Ash Borers may also attack American fringetrees, small deciduous trees native to the eastern U.S.
What do EABs look like?
Adult EABs will be easier to spot than EAB larvae, which bore inside of the trees.
As adults, EABs are:
▪ Metallic green in color while their wing covers are down. When their wing covers are lifted up, their bodies are revealed as metallic red and purple.
▪ About a half-inch long.
As larvae, EABs:
▪ Are cream-colored.
▪ Might look similar to a worm, with bell-shaped body segments.
▪ Can grow to be 1.25 inches long.
How do EABs attack and kill ash trees?
Adult EABs are active in the spring and summer. They live for three to four weeks, during which time they feed on ash tree leaves, mate and lay eggs on the tree bark.
About three weeks later, the eggs hatch, and young larvae bore into the tree. Once inside, they feed on the inner bark, or phloem, and outer wood, or xylem — both parts of the tree’s nutrient transportation system.
The larvae create snake-like tunnels in the tree, preventing the flow of water and nutrients to the rest of the tree. This causes the tree’s branches to die and the canopy to thin, likely resulting in the eventual death of the tree.
The larvae become inactive during the winter, and pupate, or mature, the following spring. After pupating, which takes about a month, the bugs emerge as adult EAB, and the life cycle — and the tree-killing — starts again.
EABs go through one generation, or life cycle, every year. Ash trees typically die within five years, or five EAB generations, of initial infestation.
How can I tell if my ash trees are infested?
There are several signs that your ash trees might be infested with EAB:
▪ Increased woodpecker activity. Woodpeckers like to fleck off the bark of ash trees and eat the larvae beneath the surface.
▪ Canopy thinning. The canopy is the uppermost part of a tree, above the trunk, where the branches and leaves are. If the canopy is thinning, it means that fewer leaves are sprouting and the branches are dying off.
▪ Branch dieback. Because fewer nutrients are reaching the tree, branches may begin to progressively die off — typically starting at the tips, and eventually killing entire branches.
▪ “D”-shaped exit holes. When adult EABs emerge from ash trees, they leave a hole in the shape of a capital “D.” The holes are typically about one-eighth of an inch.
▪ Bark splitting. The larvae feeding inside the tree may cause the bark on the outside of the tree to split vertically.
▪ Epicormic sprouts. Also known as “water sprouts,” these are growths that occur at the bottom of a tree. Epicormic sprouts are not exclusive to ash trees and EAB infestation, but are a generally sign of stress in the tree.
If you suspect ash trees in your yard or on your land may be infested with EABs, you can contact your local N.C. Forest Service county ranger for a diagnosis or tree management advice.
Licensed arborists may also be able to help. You can find arborists near you through a variety of professional organizations and online, including at treesaregood.org/findanarborist.
Can I save my ash trees once they’re infested?
EABs begin feeding from the top of the tree and work their way down each generation.
By the time symptoms reach eye-level for humans — about one to two years after initial infestation — it is often too late to save the tree.
The general rule of thumb, Oten said, is that the tree cannot be saved if it’s lost more than half of its canopy.
If more than half of the canopy remains, you may be able to treat the tree, but it could take more than two years to see improvement.
When should a diseased tree be removed?
If an ash tree in your yard is dead, it is best to have the tree removed. Dead trees can be a safety hazard, especially in urban or densely populated areas, as they can fall without warning.
“If the tree is beyond saving, and it’s near where people are or where structures are, they should absolutely be removed because those pose a risk to people and things around it,” Oten said.
If you remove a dead ash tree, it’s a good idea to plant a different species of tree in its place to prevent EABs from killing your new tree. If you’re unsure of which tree species are best for your soil, Oten suggests visiting a local plant nursery to ask for advice.
In natural forest areas, it may be better to leave a dead ash tree alone, as it can continue to provide habitat for wildlife and provide natural resources for decomposers in the ecosystem.
How can I treat and protect my ash trees?
If you have ash trees in your yard, it’s important to routinely monitor them for any signs of infestation or deterioration. For example, you may notice fewer leaves emerge in the canopy in the spring.
In most cases, it’s best to be proactive and treat your ash trees before they become infested.
Currently, Oten said, the only option to treat ash trees is to use chemical insecticides.
“If your ash trees aren’t treated with a chemical, then in all likelihood, there’s a very, very, very good chance that they will die,” Oten said.
The insecticides can be applied:
▪ Through a systemic injection. In this method, the chemicals are injected into the tree near the bottom using equipment similar to an IV in humans. The xylem carries the insecticide up and throughout the tree. The insecticide must be applied by a licensed applicator every two to three years.
▪ Through a soil drench. Soil drenches are less expensive than systemic injections, but they can pose a risk to other plants surrounding the ash tree, Oten said. The chemicals used in soil drenches can also be less effective than those used in injections.
Oten recommends treating your trees with an injection if possible.
There are currently no viable options for treating ash trees in the forest setting, Oten said, but researchers at N.C. State and the N.C. Forest Service are studying whether “natural enemies” of EABs, such as parasitoid wasps, can be used as a long-term, sustainable approach.
How can I prevent EABs from spreading?
EABs only spread naturally about five miles every year by flying.
The greater risk comes from human activity that spreads the pests farther, such as moving infested firewood. Larvae living in the trees will not be visible, so cutting down a tree and transporting it could lead you to unknowingly infect trees in a new area.
▪ To prevent EABs from spreading in this way, it is highly recommended to burn untreated firewood only within 50 miles of where it was cut.
▪ If you need to use firewood for purposes such as camping, Oten recommends cutting firewood when you arrive to your destination — not bringing it with you.
“If everyone does that, then we can reduce the spread of all of these different invasives that are spread in firewood,” Oten said.
How to contact the NC Forest Service
To contact the NC Forest Service (District 11) by phone: 919-732-8105
To contact District Forester Jennifer Roach by email: jennifer.roach@ncagr.gov
This story was originally published November 2, 2021 at 7:15 AM.
