Unfortunately, an insect is killing our hemlock trees. 

The woolly adelgid is a tiny, aphid-like insect that is ravaging our hemlock trees. 

It attacks large native hemlock forests as well as the hemlock landscape trees in your yard. 

The hemlock is critical for the overall health of our forests and river ecosystems.

Hemlocks are one of the most popular trees planted in parks and yards, so this problem can hit close to home.

The woolly adelgid is easiest to spot in spring and summer. 

It attacks new growth, during the setting of needles, eventually causing those needles and soon, the entire branch to die. 

As the infestation grows, the tree eventually starves to death.

Here’s what to look for, depending on the season:

• Spring, orangey brown eggs

• Early summer, tiny reddish-brown insects, they almost look like pepper sprinkled on the stems.

• Summer, the young insects spin a little white nest made of a waxy, woolly-looking substance. The small white nodules will be visible at the base of the needles. This is the easiest way to identify the pest.

• Fall, during the heat of summer, the woolly adelgid goes dormant. They come back out and start feeding in the fall and over the winter.


How to control 

the woolly adelgid

Insecticide. Unfortunately, the only option is an insecticide, and the most effective options aren’t the most eco-friendly ones. So, read the application directions and use caution when treating your trees.

Begin by treating the trees that are the healthiest, the most integral to your landscape design, and the farthest from streams and water sources. 

It’ll take a month or so to see a change, and you will have to continue monitoring your trees. 

If the treatment is effective, you should see the insects disappear and new needles start to grow.

Soil treatment. Soil treatment, or soil drenching, is considered the most effective method and simplest method of treating the woolly adelgid in home landscapes.

1. Look for an insecticide with the active ingredient imidacloprid. It’s sold under a variety of names, including Bayer Advanced Tree & Shrub Insect Control and Ortho Max Tree & Shrub Insect Control. You will need the large bottle of concentrate, rather than the ready-to-use spray bottle.

2. Dig a circular trench around the tree about a foot from the trunk of the tree and approximately 3 inches deep.

3. Mix the concentrate according to the container directions, and pour into the trench. The sap of the tree then becomes poisonous to the adelgid which drinks hemlock sap as its food. Soil drenching can take several months to be effective.

Natural predators. Since large forests obviously can’t be treated with insecticides, researchers are working to develop natural predators to release for large scale control of the woolly adelgid.

Professional options. If your trees are near water, or if the soil is too rocky to dig trenches, licensed professionals may have a couple more options such as high-pressure sprayers and water safe trunk injections.

The Environmental Committee will continue to monitor this concern and provide updates as necessary.

Further information can be found at saveourhemlocks.org, Hemlock Woolly Adelgid: A Threat a University Tennessee Agricultural extension publication SP503-G and panthercreekforestry.com.

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