What’s looming on the horizon: A closer look at emerging forest pests encroaching on the North Carolina border

by | Apr 1, 2024

Nonnative invasive species are a hot topic these days, and rightfully so as they are considered one of the greatest threats to biodiversity. News headlines are filled with stories of emerald ash borer (EAB) causing widespread decline of ash trees, zebra mussels clogging waterways, Bradford pear and tree of heaven choking out forests and feral hogs plowing through an area consuming anything in their path.

Over the past centuries, globalization has led to the intentional and unintentional introduction of more than 37,000 species beyond their natural ranges. Over time, more than 3,500 species have been introduced and classified as invasive, wreaking havoc on their new environments by outcompeting native wildlife, disrupting ecosystems and causing significant economic damage. North Carolina alone spends an average of $1.6 million annually on invasive species removal (2020), and this does not account for the cost of research, the financial burden for private landowners, the loss of biodiversity and aesthetic decline of natural areas.

So, what’s looming on the horizon for North Carolina?

Asian longhorned beetle

Adult ALB emerged from exit hole in Red Maple (Acer rubrum). Photo by Joshua P. Basham.

The Asian longhorned beetle (Anoplophora glabripennis, or ALB) is no new threat. Although it remains undetected in the state, a disjunct population was discovered outside of Charleston, SC, in 2020, indicating that it’s something North Carolinians should remain cognizant of. ALB is native to China and Korea and feeds on roughly 29 hardwood species, with maple being the preferred host. It was first discovered in Brooklyn, NY, in 1996 and has since been found in other parts of the Northeast, killing valuable shade trees and forest trees of economic value such as sugar maple (Acer saccharum).

Females chew dime-sized notches in the bark of host trees to lay their eggs. Following hatching, larvae primarily consume sapwood, disrupting vital water and nutrient transport within the tree. As they mature, larvae migrate deeper into the heartwood, creating tunnels as they feed. This severely compromises the structural integrity of the host, making it more vulnerable to breakage, which poses a significant hazard during wind or ice storms.

Once an individual tree is infested, there is no remedy, although eradication of ALB is possible with early detection and rapid response. Infested and high-risk trees are removed and destroyed by chipping, a method developed by the ALB Eradication Program, which has proven successful in several locations in the Northeast. Students at N.C. State University are actively investigating eradication methods in South Carolina tailored for southeastern bottomland hardwood forests, as the distinct climatic conditions pose a novel set of challenges for professionals when compared to the hardwood forests of the Northeast.

What can you do? Familiarize yourself with the beetle’s appearance and be on the lookout for the following signs and symptoms of an ALB infestation:

  • Perfectly round exit holes about the width of a pencil eraser, often oozing sap.
  • Frass, excrement that looks like stringy sawdust around the base of an infested tree.
  • The presence of dime-sized egg niches on bark.
  • Weakened branches prone to breakage.
  • Abnormally early fall coloration.

Elm zigzag sawfly

EZS larva feeding on American elm leaf (Ulmus americana). Photo by Owen Clarkin.

The elm zigzag sawfly (Aproceros leucopoda or EZS) is native to China and Japan, and as its name suggests, infests elm trees (Ulmus spp.), leaving behind zigzag patterns in the leaves as the larvae feed from the edge of the leaf toward the midvein. While established in Europe since 2003, the exact origin of the EZS population present in North America remains unclear. Since its initial detection in Canada in 2020, the sawfly has spread to several states in the Northeast. The first confirmed sighting of EZS in North Carolina was in August 2022 near the border of Stokes and Surry counties, marking the southernmost extent of the EZS spread. Much like the Asian longhorned beetle, their spread has been spotty, suggesting that humans may be aiding in their extended dispersal.

EZS larvae are capable of significant defoliation, sometimes consuming more than 90% of leaves in heavily infested trees. They are strong fliers who are known to travel up to 56 miles annually, reproduce asexually and have multiple generations each year. All of which may be significant factors contributing to their invasive potential. However, there’s currently no evidence to suggest EZS is causing mortality of elm trees in North Carolina. While healthy trees can typically survive repeat years of defoliation, the long-term effects on their resilience are still unknown. Students at N.C. State University are actively monitoring the phenology of EZS in the southeast, investigating alternate hosts and assessing the potential ecological impacts this pest may have on our forests and urban areas.

As of 2023, the infestation is currently thought to be limited to Stokes and Surry counties, but ongoing surveys will determine the extent of the infestation. Though the adult may be difficult to distinguish from other native sawfly species, their larvae’s distinctive zigzag feeding pattern on elm leaves offers a dead giveaway. It’s important to note that other sawfly larvae in the subfamily, Sterictiphorinae, create a similar feeding pattern, but on the leaves of Prunus species like black cherry (Prunus serotina) rather than elm.

Beech leaf disease

Leaf banding associated with beech leaf disease damage. Photo Kristen Wickert, USDA Forest Service, Bugwood.org (left). LCM, the foliar nematode associated with beech leaf disease. Photo by Paulo Vieira, USDA Forest Service (right).

In Western North Carolina, the primary threat to American beech (Fagus grandifolia) has been beech bark disease (BBD). However, beech leaf disease (BLD) is an emerging forest threat that has been gaining ground in the Northeast, causing dieback and widespread mortality of American beech at an accelerated rate. To put this into perspective, BBD has spread through much of the northern extent of the American beech range over a span of more than two decades. BLD has spread across much of this region in less than half that time.

BLD was first detected in Lake County, Ohio, in 2012. The culprit is a newly recognized subspecies of foliar nematode, (Litylenchus crenatae mccannii or LCM), which was discovered from leaf samples collected in 2017. By 2020, the disease had spread to eight states and into Canada. However, researchers are making headway in understanding the life cycle of LCM and describing the connection between the nematode and the occurrence of specific symptoms associated with BLD. By 2021, BLD was detected in neighboring Virginia and, in 2023, in Maryland, Delaware and Vermont, bringing the current total to 14 states.

Much remains unknown about this newly identified disease including its origin, mode of transmission and potential management options, which are the subject of ongoing research. What we do know is that thousands of LCM overwinter in beech buds, feeding on the developing leaf tissue. Infected leaves emerge in the spring with the following symptoms:

  • Dark green banding between leaf veins, often the first symptom.
  • Cupping: leaves that are curled rather than having a smooth, flat shape.
  • Leathery leaf texture.

It’s important to note that these symptoms don’t worsen throughout the growing season—the harm is inflicted during winter. Additionally, while American beech trees typically hold on to their dead leaves through winter, a phenomenon botanically known as marcescence, affected trees may also experience premature leaf drop, leaving trees abnormally bare throughout the summer.

If you suspect any activity from the invasive species mentioned above on your property, the N.C. Forest Service encourages you to report your observations by contacting your local county ranger’s office. To find contact information for your county ranger, visit  https://www.ncforestservice.gov/contacts.

 

Sources:

Eiseman, Charles. (2015). On the Distinctive Feeding Pattern of Sterictiphora Billberg (Hymenoptera: Argidae) Sawfly Larvae. Proceedings- Entomological Society of Washington. 117. 65-67. 10.4289/0013-8797.117.1.65.

Jenkins, D., Johnson, M., Waite, F., & Whitesides, D. (2024, March 1). Asian longhorned beetle in South Carolina. South Carolina Forestry Commission. https://www.scfc.gov/wp-content/uploads/2021/06/asianlonghornedbeetle.pdf

North Carolina Department of Agriculture and Consumer Services. (2020). North carolina department of agriculture and consumer services’ study of state-managed properties. https://webservices.ncleg.gov/ViewDocSiteFile/28290

Oten, K., Bertone, M., & Serpan, D. (2022, August 31). Elm Zigzag Sawfly. NC State Extension: Invasive Forest Pests. https://content.ces.ncsu.edu/elm-zigzag-sawfly

Reed, Sharon. (2024, January 17). Solving the mysteries of beech leaf disease: 6 years of partnerships. Invasive Species Centre. https://www.youtube.com/watch?v=KqiOxQTEVjg&t=539s