Hemlock woolly adelgid (HWA) (Adelges tsugae) is a small aphid-like insect native to Asia that is now threatening eastern hemlock (Tsuga canadensis) and Carolina hemlock (Tsuga caroliniana).
Impacts: HWA threatens hemlock trees, genus Tsuga. HWA feeds on hemlock tree sap by attaching their specialized mouthparts into the base of hemlock needles. This triggers a defense in host trees to “wall off” these incisions (similar to a scab growing over a cut) and over time the feeding of HWA weakens the host tree and leads to tree mortality. Infested trees will display signs of distress such as needle loss, lack of regrowth in the spring, and limb damage or loss. Hemlocks that experience environmental stresses, such as drought, are more susceptible to an HWA infestation. In general, untreated hemlock infestations will cause host trees to die off between four to ten years, depending on infestation density and the overall health of the host tree prior to infestation.
Help keep an eye out for hemlock woolly adelgid (HWA) while you’re out hiking and snowshoeing. The story-map below showcases hiking trails where there are hemlock trees to monitor for signs of HWA. Detecting hemlock woolly adelgid early on will aid spread prevention and control efforts for this invasive pest.
If you see signs of HWA presence, report observations via www.iMapinvasives.org
or contact the NYSDEC Forest Health Information Center: 1-866-640-0652
*Record the GPS coordinates of the location & take clear photos of the suspected signs
Stress on infested hemlocks can be reduced by pruning dead or dying branches and watering trees during dry periods. This will reduce the chances of infestation by HWA. Note: Avoid fertilizing hemlocks with a nitrogen fertilizer as it will encourage HWA reproduction and survival.
Individual trees can be treated with a systemic insecticide, applied as a soil drench or basal bark spray. Once applied, the treatment can provide years of protection for the tree.
Hemlock foliage may also be treated with horticultural oils and insecticidal soaps as long as the trees are small enough to be saturated, ensuring that the HWA has been exposed.
NYS Hemlock Initiative: HWA Management
Several HWA predators, including beetles and fungal pathogens, are being tested for effectiveness in treating infested hemlocks on a large scale. While more research is needed to assess long-term feasibility, studies have shown this to be a promising method of controlling HWA.
USDA Forest Service: http://na.fs.fed.us/spfo/pubs/pest_al/hemlock/hwa05.htm
Penn State College of Agricultural Sciences: Entomology Department: http://ento.psu.edu/extension/factsheets/hemlock-woolly-adelgid
The Nature Conservancy and Catskills Invasive Species Partnership: Catskills Hemlock Health-TNC Final Report 2014
Eastern Connecticut Forest Landowners Association Wolf Den Land Trust: http://www.ecfla.org/articles/adelgid.htm
Photo Credits: Title photo: Connecticut Agricultural Experiment Station Archive, Connecticut Agricultural Experiment Station, Bugwood.org. Adult, nymph, and egg photos: UMass Amherst Center for Agriculture Food and the Environment, https://ag.umass.edu/fact-sheets/hemlock-woolly-adelgid. Crawler photo: Shimat Joseph, University of Georgia, Bugwood.org, Pennsylvania Department of Conservation and Natural Resources – Forestry Archive, Bugwood.org.