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Hemlock Woolly Adelgid (HWA) ( Adelfes tsugae ). Tsuga spp. Kingdom – Plantae Division – Pinophyta Class – Pinopsida Order – Pinales Family Pinaceae Tsuga heterophylla western hemlock
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Tsuga spp. Kingdom – Plantae Division – Pinophyta Class – Pinopsida Order – Pinales Family Pinaceae Tsuga heterophylla western hemlock Tsuga is a genus of conifers known as hemlocks. There are four species in North America, and four to six in east Asia.
Hemlocks • Medium-sized to large evergreen trees, ranging from 20–60 m tall, with a conical to irregular crown, with the latter occurring especially in some of the Asian species. The leading shoots generally droop. The bark is scaly and commonly deeply furrowed, with the color ranging from grey to brown. The branches stem horizontally from the trunk and are usually arranged in flattened sprays that bend downward towards their tips
Hemlocks that are affected tend to have a grayish-green appearance
Scientific name: Adelges tsugae Native to: Asia – Japan and China Date of U.S. introduction: 1920s Pacific Northwest; 1951 – eastern United States Means of introduction: Arrived accidentally in shipments from Asia Impact: Destroys eastern hemlock trees by sucking their sap
HWA Life History HWAs are aphid-like insects, getting their name from their woolly white appearance and host preference. Have a very complex life cycle, producing two generations per year. Eggs are a brownish-orange, wrapped in a white fluffy substance secreted from the female. Reddish-brown nymphs hatch, with a thread-like mouthpart capable of branch piercing hemlocks to suck the sap. Adults are reddish-purple and have two pairs of wings; those that are wingless stay on the hemlock host to produce 50-300 eggs. Both the adults and nymphs suck sap from young twigs, which causes the trees to die in only a few years
Spread • In North America, the species lacks natural enemies that are needed to stop it from spreading. Much of the spread is pushing westward from the eastern United States. • Spread occurs by a number of different means, including wind, birds, and mammals. Human influence impacts spread rate, through incidental transport and movement of nursery stock.
The hemlock woolly adelgid has already affected the Blue Ridge Parkway for about 10 years, and the Shenandoah National Park since the late 1980s. Within these two areas over 80% of hemlocks have already died due to infestation. The National Park Service is working to control the rate of spread of the adelgid with various treatment types. Smoky Mountain Impacts
Foliar Treatment Hemlocks found along developing areas or backcountry sites are being treated with an insecticidal soap or horticultural oils. This spray is able to smother and dry-out the adelgids on contact, and the equipment is able to spray up to 80 feet into the canopy. This particular treatment only kills the insects that are present on the tree when the application was applied.
Systemic Treatment • Trees too tall for the spray or those near campsites are treated either by soil drenching or by injecting the insecticide directly into the trunk. • Soil drenching is proving to be the most effective. Soil drenching is temporarily removing organic matter or duff and then pouring a mixture of imidacloprid (insecticide) and water on the bare ground. Once complete, the ground is covered back up. • Results have been dramatic, since the trees recover their color and produce new growth
Predator Biocontrol (2002+) Predators introduced for control in the eastern United States, left to right (origin): Sasajiscymnus tsugae (Japan), Scymnus sinuanodulus (China), and Laricobius nigrinus (western North America)
Mechanically removing adelgids • During this treatment, both the eggs and crawlers of the hemlock woolly adelgid are dislodged from any young hemlock twigs by either wind or rain. • Directing a long strong stream of water at infested branches periodically during April – June can also remove the adelgid from its tree. • Most that get swept away are not able to make it back to the tree, and die. • Planting resistant hemlock species • There are a few species that are resistant to this pest, of them the western hemlock is the most similar to the eastern hemlock. • Though the adelgids will infest the resistant species, they seldom reach densities that are high enough to cause any serious injury. • By planting these resistant species, it could reduce the impact of the adelgid in the ornamental landscape.
Ways to help • There are many sites that are trying to raise money to help save the “redwood of the east”. • One of these sites being funded through the Save the Hemlocks Initiative. If you would like to get more information from this group you can call (865) 453-2428 or visit www.saveourhemlocks.org to learn more.
