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What is white, fluffy and woolly all over?

August 21, 2012
BY HILARY SMITH , Adirondack Daily Enterprise

The hemlock woolly adelgid sounds too cute to be a tree killer, but it is. Luckily our cold winter temperatures have held this forest pest at bay, for now; unfortunately, other parts of the state are not so lucky.

I learned about invasive forest pests when the Adirondack Park Invasive Plant Program broadened its mission beyond plants, and I began taking extra care to look for signs and symptoms of unwanted forest invaders.

As a homeowner, I became even more aware of the health of trees. Our property is forested with some ornamental but mostly native trees. They provide an important vegetative screen for privacy, welcomed shade during hot summer days, year round aesthetic beauty and habitat for wildlife.

Article Photos

Hemlock woolly adelgids lay white, cottony egg sacs on the underside of hemlock needles.
(Photo — John A. Weidhass, Virginia Polytechnic Institute and State University,

I am grateful for the trees on our property, and when they begin to show signs of decline, I take notice. For instance, the tall eastern white cedar near the driveway is splitting in two, as is the majestic sugar maple which buffers the noise from the road. Insect holes ring the trunk of our colorful, aged mountain ash that bears striking autumn fruit. And, our beech trees suffer from beech bark disease. Despite these afflictions, the trees are surviving, and, along with our healthy trees, provide much benefit and enjoyment.

Knowing that the emerald ash borer (EAB) is on the move, I searched for ash on our property. I found 20 trees and am preparing for their loss when hungry EABs eventually find the Adirondacks. Invasive forest pests and pathogens, like EAB, can spread swiftly through forests and cause tree death in fewer than five years.

Hemlock woolly adelgid (HWA) is another such pest that can cause mortality to its host, the Eastern hemlock, within four to 10 years. We do not have hemlock on our property - a relief if the adelgid arrives - however, hemlocks are a vital component of Adirondack forests and much could be lost to an HWA invasion.

The Eastern hemlock is one of the longest-lived tree species - living up to 800 years in eastern North America. They typically grow along steep slopes where few other trees can grow. This helps maintain erosion control and water quality. Their dense canopies are ideal habitat for birds and other wildlife, and the shade they provide along streams and rivers is essential for many cold water fish species, such as brook trout. But, the hemlock woolly adelgid can change all of that.

Related to aphids, the adelgid extracts sap and nutrients from hemlock foliage, which prevents growth, causing needles to discolor from deep green to grayish green and to drop prematurely. The loss of new shoots and needles seriously impairs tree health.

Extensive hemlock mortality has already occurred from Georgia into the Northeast. Native to Japan, HWA was first discovered in New York in 1985 in the Hudson Valley. It has since spread north and west to the Catskills, the Capital Region and even the Finger Lakes and other parts of western New York.

HWA travels long distances by wind, birds, other wildlife and the movement of infested wood by humans. Although limited by colder temperatures in our region now, projected increases in winter temperatures may promote the range expansion of HWA into more northern hemlock forests, areas previously considered unsuitable for its survival.

Join us in combating this invasive insect. Use firewood local to the area you are visiting to help stop its spread. Also, keep watchful eyes on our hemlocks. Hemlocks are evergreen with needles that are flat, one-half to two-thirds inches long and have two white parallel lines on their undersides. Look for signs of stress, loss of needles and small, white, woolly masses, which are the adelgid's egg sacs, attached to undersides of twigs near the base of the needle.

Since HWA is not here yet, early detection is the best defense. To report sightings, contact your county's Cornell Cooperative Extension or the Adirondack Park Invasive Plant Program at 518-576-2082. Learn more about HWA biology, detection and management at

Eye on Invasives is a biweekly column that spotlights a top invader when it is easiest to identify. Hilary Smith directs the Adirondack Park Invasive Plant Program, a partnership program housed at the Adirondack Chapter of The Nature Conservancy in Keene Valley. Find out more about this award-winning program online at



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