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A Short Guide to the Hemlock Woolly Adelgid

Do you have any eastern hemlocks (Tsuga canadensis) or Carolina hemlocks (Tsuga caroliniana) growing in your landscape? These trees are considered keystone species of the forest and woodlands because they're slow-growing, towering evergreens that live up to 500 years. Hemlocks shade forest streams and shelter nesting birds.

Unfortunately, wherever hemlock trees grow in the eastern U.S., the woolly adelgid (Adelges tsugae) is sure to be thriving. You can help stop the spread of the hemlock woolly adelgid (HWA) on your property and in our forests. Here's some information to get you started.

The HWA Is an Invasive Insect Species

According to experts in entomology and plant pathology, around one-fourth of east-coast hemlocks have been infested with the HWA pest. This tiny insect is an Asian species that was introduced to the Pacific Northwest in the 1920s.

HWA was first reported in Virginia as early as 1951. By 2002, the pest was infesting hemlocks in the Great Smokey Mountains National Park. Today, the HWA has killed hemlock trees from Georgia to Nova Scotia.

Invasive species are especially destructive if the area has no natural predators of the insect pests. For example, in Asia and western states, the hemlock trees are protected by beetles and other insects that feast on the HWA to keep numbers in check.
Other factors that increase the destruction of HWA infestations include:
  • Damage from other insects
  • Drought conditions
  • Fungi infestations
  • Mild winters

HWA pests are protected from insecticides by their own waxy secretions. The HWA also injects toxins into trees to accelerate the trees' demise. Their main method of killing trees is simply feeding off hemlock tree sap from the bases of needle growth.

The Pests Are Tiny but the Nests Are Obvious

Individual HWA pests are nearly microscopic in size at just under 1/16-inch long. The small insects are colored reddish-purple. They're as tiny as aphids, but they give telltale signs of their presence.

Bend a hemlock branch gently to look at the underside of the outermost needles. Look for small, white, cotton- or wool-looking bumps or growths at the bases of needles. Inside these growths - which are actually filaments of wax - are hundreds of eggs that emerge and begin feeding.

Growths are normally seen from late fall to early summer. Other signs of HWA infestation include:
  • Brown and dying branch tips
  • Thinning and dieback of crown
  • Changing color from bright to dull green

Remember that some of the signs above can be symptoms of other tree pests and diseases. If you aren't sure about HWA on your hemlocks, contact your tree service to schedule a hemlock inspection and accurate diagnosis of the problem.

The HWA Is Battled on Many Fronts

Most HWA larvae become sedentary sap suckers who can't leave their hemlock host on their own. Some HWA larvae become winged, but they don't find what they need to colonize and soon die. Since the individual insects themselves have restricted movement, the spread of HWA is accomplished by:
  • Displacement from wind and storms
  • Hitchhiking on people and mammals
  • Attachment to migratory birds
  • Infestation from firewood and nursery plants

You can help stop the spread of the pest by being careful around hemlocks when you're taking part in hikes and other activities in the forest. Thoroughly clean and vacuum equipment, clothes, and shoes that may have come in contact with the pest.
Wash your pets after forest trips too. Remove bird feeders from around your hemlocks, and water the trees well during dry periods to help protect your trees.

A natural predator of HWA has been introduced to combat the pest. The results are inconclusive at this time. Ask your tree service professional for more information.

If your tree service confirms the diagnosis of HWA, they will tell you the best options for your tree's health and the health of your community. In some cases, soil and tree pesticides may be administered. Sometimes, you need to have the tree removed before it becomes a hazard.

Whether you need a diagnosis or the removal of a hemlock tree, contact Joe Webster Tree Care, Inc. today. We offer a full line of professional tree services in the Huntsville, northern Alabama, and southern Tennessee regions.
Joe Webster Tree Care, Inc.
219 Goodman Road SE,
Huntsville, AL 35803

Phone: 256-539-2150


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