By June 14, 2017 Read More →

Don’t let HWA Pull the Wool Over Your Eyes!

Great Sacandaga Lake – June 6th, 2017. [Photo: Emily Pomeroy]

On June 6th, I joined Forest Entomologist, Dr. Mark Whitmore, along with the Adirondack Park Invasive Plant Program’s (APIPP) Terrestrial Invasive Species Coordinator, Zachary Simek, New York State Department of Environmental Conservation (DEC) Forest Ranger, Andrew Lewis, and DEC Forest Health Research Scientist, Jessica Cancelliere, on Great Sacandaga Lake to survey for hemlock woolly adelgid (HWA). We circumnavigated the lake’s shoreline inspecting hemlocks for any suspicious damage or lack of spring growth which may indicate an infestation. Great Sacandaga Lake was the second Adirondack lake to be surveyed this season – Lake George had been surveyed the previous day, and thankfully no HWA infestations were discovered. But, the clock is ticking. The Adirondacks contain the highest density of hemlocks of anywhere in New York State and HWA has been moving further north each year due to milder winters. Just a few weeks ago, a new infestation of HWA was discovered just 20 miles south of Great Sacandaga. HWA is commonly spread by birds which use shoreline trees as stopping points during their daily and seasonal migrations, making lakeside hemlocks a likely location for new infestations. Once a hemlock forest becomes infested, HWA will kill the trees over a matter of years. Dr. Whitmore leads the New York State Hemlock Initiative, a program based at Cornell University that aims to conserve the state’s hemlocks by conducting research, implementing outreach, and applying management strategies.

Why are Eastern hemlocks so important to protect?

The Adirondack region is home to millions of Eastern hemlock, which are considered a keystone or foundation species.  This simply means that they are a critically important component of ecosystems that many other organisms rely on for survival. For example, hemlocks provide cool shade over streams, thus sustaining suitable habitat for brook trout. They also provide a source of shelter and food for many species of wildlife such as ruffed grouse, white-tailed deer, and many species of birds.  Hemlocks have and continue to be important to people as well.  The bark of Eastern hemlock is naturally high in tannins, and was historically harvested and used to tan leather products. Today, Finch Paper Co. uses about 50% hemlock for its paper production. Many land owners plant hemlocks as a decorative hedge, and in the Adirondacks it is considered one of the region’s most iconic trees.

What is Hemlock Woolly Adelgid and what does it look like?

The protective wool produced by HWA on the underside of a hemlock branch. [Photo: Emily Pomeroy]

Hemlock woolly adelgid is a small, aphid-like insect native to Asia that was accidently introduced to the United States in the 1950’s, likely through imported nursery stock. They derive their name from the characteristic white, woolly coating that they create to protect themselves and their eggs from the elements. Inside, the adults themselves are black and are extremely small and difficult to see. Each adelgid inserts its mouth piece and feeds on the tree’s fluids at the base of a needle where it attaches to the twig. In response, the tree attempts to wall off the wound. As populations of the insect increase, this response eventually cuts off all water and nutrient circulation within the tree, thereby killing it. In some instances, HWA is able to kill the tree in as little as 5 years although it usually takes 10 or more in colder climates.

Why survey shoreline hemlocks in the spring?

Dr. Mark Whitmore, Andrew Lewis, and Jessica Cancelliere use binoculars to inspect an unhealthy hemlock for signs of HWA. [Photo: Emily Pomeroy]

Through his research and observations, Dr. Whitmore has found that many new infestations of HWA tend to appear along lake shores. He has discovered a few new infestations isolated on a single overhanging branch great distances from the next closest outbreak, a phenomenon he refers to as the “skipping stone” effect. He believes this is a result of transport by birds, as they travel long distances, and have the ability to transport the insect from one area to another on their feet or in their feathers. Birds tend to gravitate toward bodies of water, making lakes and rivers priorities for survey and likely early detection points.

New spring growth on an Eastern hemlock. [Photo: Emily Pomeroy]

In the spring, from June through early July, the tips of healthy hemlock branches produce bright green shoots. An absence of these shoots on any branch could indicate a sick or dying tree, a warning sign that HWA may be feeding on the tree. Hemlocks that appear to be unhealthy, such as those with dead branches or discoloration are also suspect. Binoculars can be used to confirm the presence of new growth that may be hard to see from the ground or water. If a tree lacks new spring growth it can be more thoroughly inspected for the presence of woolly masses which would indicate HWA presence. We deployed this technique on large portions of Great Sacandaga Lake and Lake George and hope to complete surveys of the entire shoreline over the coming weeks.

What can be done to prevent the spread of hemlock woolly adelgid and manage it once it is discovered?

Besides being transported by birds, HWA can be transported long distances in contaminated hemlock nursery stock. You can avoid moving HWA unintentionally by purchasing locally sourced or inspected, and innocuous trees. There are currently also several management options for treating localized infestations of hemlock woolly adelgid once discovered. The most frequently used treatment is to apply a combination of two pesticides. Imidacloprid, can be sprayed onto the lower bark, or injected into the tree, and can remain effective for up to 7 years.  However, Imidacloprid can take a long time to move up to the crown of the tree, and may not beat the adelgid in its race to the top. Therefore, it is used in conjunction with another pesticide with active ingredient Dinotefuran. Dinotefuran is sprayed onto the lower bark of the tree and moves up the tree very quickly, but only remains effective for one year. The combined use of both ingredients ensures that the entire tree is protected immediately, and remains protected for several years. The pesticide contained within the tree kills HWA when it attempts to feed. These pesticide applications should only be performed by a New York State certified pesticide applicator.

Biological control methods for HWA are also being researched. Currently, the beetle Laricobius nigrinus or “little Larry” has been shown to be a successful predator of the adelgids.  These beetles have been released in the Finger Lakes region over the past 9 years.  Two silverfly species Leucopis argenticollis and Leucopis argenticollis have also been released in New York within the past two years, and the predaceous fly larvae appear to be effective at controlling HWA. These biological control options have the potential to provide widespread, sustained control of HWA, but they are often difficult to capture in the wild and expensive to purchase or rear. Mark and his team of researchers have recently secured funding to establish a permanent biological control rearing facility at Cornell which will hopefully make these HWA predators more widely available for release over the coming years.

What can you do if you see hemlock woolly adelgid?

If you believe you have discovered an infestation of hemlock woolly adelgid in the Adirondacks, please report your findings to APIPP.  Be sure to take pictures of the suspected hemlock, its branches, as well as any woolly masses, and record the location.  Findings can be reported either directly to APIPP by calling (518) 576-2082, through APIPP’s website under “Report an Infestation”, or through iMapInvasives.

 

Sources

https://www.na.fs.fed.us/fhp/hwa/pubs/95_proceedings/Quimby.pdf

https://plants.usda.gov/plantguide/pdf/cs_tsca.pdf

https://blogs.cornell.edu/nyshemlockinitiative/

 

[By: Emily Pomeroy]

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