Hemlock Woolly Adelgid


Hemlock Woolly Adelgid on a branch Hemlock Woolly Adelgid Impact Area Hemlock Woolly Adelgid nymph HWA predator beetles



In the early 1950’s, a small, aphid-like insect was first observed feeding on hemlock in Virginia. This insect was the hemlock woolly adelgid (HWA), Adelges tsugae (Annand), an exotic pest native to Japan and China. The HWA has since spread to 17 eastern states where it attacks two species of hemlock – the eastern hemlock and Carolina hemlock. The HWA is responsible for extensive mortality and decline of hemlock trees in the eastern United States. The insect has steadily spread from its point of introduction and is a serious threat to survival of hemlocks throughout eastern North America. The potential ecological impacts of this exotic insect pest can be compared with those of chestnut blight. Forest Health Protection has taken an aggressive approach in dealing with this exotic insect pest.

Key Issues:

Continued Spread

  • Half the range of hemlock in the East is now infested.
  • The entire range of eastern hemlock is at risk.
  • In 2010 HWA has been found in North Carolina, Georgia, Tennessee, Kentucky, Virginia, and South Carolina.

Resource Impacts

  • Extensive tree mortality and decline are found throughout the infested region.
  • Severe impacts to date are in Virginia, North Carolina, Tennessee, Georgia, New Jersey, and Connecticut. In New Jersey and Virginia hemlock mortality in heavily infested stands is estimated at 90 plus percent.
  • Scientists predict significant tree mortality throughout the range.

Project Highlights

  • R8 FHP is an active partner in the HWA management initiative. The annual budget for this initiative has averaged between $2.5 and $3.5 million. This initiative was developed under the leadership and direction of FHP staff. The list of cooperators includes dozens of State, Federal, University and Private organizations.
  • R8 has taken the lead role in the coordination, funding, and management of the HWA issue within the Southern Appalachian area. This includes advancing the knowledge base via numerous cooperative agreements with universities; implementing control strategies across boundaries; and, disseminating information to all stakeholders. FHP’s role in the coordination of activities between states, NFS, and other federal and private interest groups is critical for the management of HWA across these boundaries. Within R8 between $600,000 and $2 million per year are budgeted for the HWA program.
    • The advancement of technologies and strategies to manage HWA has been a primary focus within FHP. Some of these strategies include biological and chemical control, impact assessment, and, monitoring and evaluation.
        • The evaluation and implementation of biological controls to combat HWA is a primary goal throughout the east. FHP has provided significant funding to advance this program area. The HWA biological control program within R8 has many partners. The following are primary partners: the states of GA, NC, SC, TN,
        • KY, and VA, Cherokee, Pisgah/Nantahala, Jefferson/Washington, Sumter, Chattahoochee, Daniel Boone, NFs, Southern Research Station, Clemson University, North Carolina State University, Virginia Tech., University of Tennessee, University of Georgia, Great Smoky Mountains and Shenandoah National Parks, Blue Ridge Parkway, Friends of the Smokies, Jackson Macon County Alliance, and the Chattooga River Conservancy. Cooperative laboratories for the production of biological control agents funded by FHP are located at North Carolina Department of Agriculture in Raleigh, Clemson University, the University of Tennessee, and Virginia Tech University. FHP provides an average of $500,000 annually to these facilities.
      • Chemical control of HWA is a primary focus within FHP. There are many locations and situations where chemical controls are the best if not only option for controlling this problem. The use of chemicals in landscape setting and some forest settings is often required due to the value of the trees in question. Through suppression funding FHP provided $900,000 in 2009 for chemical control of HWA. The bulk of this funding is allocated for the National Forests and National Parks for treatments in administrative sites and recreation areas.
      • FHP is also supporting efforts to secure the genetic material for both eastern and Carolina hemlock. This project is a collaborative effort between State and Federal agencies and the CAMCORE cooperative at NCSU. This project will ensure that if HWA is successful and catastrophically impacts the hemlock resource we will have these genetic materials to work with in the future so that we might one day restore this species.
      • FHP is currently working with the state of South Carolina as they implement an ARRA project for the control of HWA on State lands. This project should help retain and or create 5-9 jobs in the affected area. The project was budgeted $179,000 and approximately 1200 acres will be treated.

Conclusions/Future direction:

FHP’s role within the context of HWA is well defined. The HWA program within R8 is following the direction of the east wide initiative. The level of cooperation and partnership within and between agencies as well as environmental groups is impressive. The HWA program could easily serve as a model on how to build an effective program from the grass roots level. With continued budgetary and political support the HWA program will continue to advance the management issues surrounding HWA and help ensure the survival of the eastern hemlock species. There may be a slight trend upward for future budget needs within the HWA arena as the range continues to expand in the southeast.


FHP Contact:

Rusty Rhea
Forest Service-USDA
200 Weaver Blvd.
Asheville, NC 28804
Phone: 828-257-4314
Email: rrhea@fs.fed.us

More Information

Hemlock Woolly Adelgid (Northeastern Area)

Hemlock Woolly Adelgid Pest Alert

Forest & Grassland Health