Web Content Viewer

Hemlock Woolly Adelgid (HWA)

hwa on conifer branch

Hemlock woolly adelgid (Adelges tsugae) is a serious pest of Eastern (Tsuga canadensis) and Carolina (Tsuga caroliniana) hemlocks of all sizes. Native to Asia, HWA was first discovered in North America in British Columbia in 1924. HWA was first reported in the eastern United States in 1951 near Richmond, Virginia. Since then it has been moving steadily through the native hemlock regions of the Appalachian Mountains, from Georgia to Maine, causing extensive mortality and hemlock decline.

In February 2012, the first infestation in a natural stand of hemlock in Ohio was discovered in Meigs County. Since then HWA has been found in hemlock stands in other eastern Ohio counties as well.

close-up of HWA

E-mail: plantpest@agri.ohio.gov


Perhaps the most recognizable sign of HWA is the cotton like excretions of wax that it produces on the underside at the base of the needles. This woolly material is secreted from pores on the body of the insect and is best seen in the spring and fall which is when HWA is most actively feeding.

Quarantine Information

Ohio quarantine regulations restrict the movement of hemlock materials from counties known to be infested into non-infested Ohio counties. Ohio’s quarantine law also requires hemlock materials grown in non-infested counties in quarantined states to be inspected before being shipped and have a phytosanitary certificate verifying that the plant material is free of HWA when entering Ohio. These requirements can be found in Chapter 901:5-48 of the Ohio Administrative Code.

Currently there are no federal regulations with Hemlock Woolly Adelgid, but several other states including Maine, Michigan, New Hampshire, Vermont and Wisconsin have established quarantines which are similar to Ohio’s regulation. Information on other state quarantines for HWA can be found at the www.nationalplantboard.org; for information about shipping hemlock nursery stock please call the Plant Pest Control Program at 614-728-6400.

HWA damage to forest

Damage and Impact

HWA damage is caused by the adelgid feeding on the sap and nutrients from the hemlock foliage and depleting its reserves. They use a long stylet type mouth part to inject at the base of the hemlock needle. Desiccated needles become discolored from a natural deep green to a grayish green and premature needle drop results. New growth is usually stunted or no new growth develops at all. Dieback damage of twigs and limbs usually occurs within 2 years of the initial infestation. The damage will start from the bottom of the hemlock tree and progress upwards. Death of the tree can occur within 4 to 5 years depending on the health of the tree at time of infestation and secondary causes that come into play as the tree is weakened.

Tree mortality can cause a dramatic shift in the composition of forest species, both plant and animal, and can affect the ecological processes that occur such as nutrient cycling, decomposition, leaching, stream temperatures and stream organisms.