Treatment helps hemlock damaged by woolly aphid | Sun Glade

Unfortunately, an insect is killing our hemlocks.

The woolly aphid is a tiny aphid-like insect that ravages our hemlocks.

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

Hemlock is essential to 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 affect near you.

The woolly aphid is easier to spot in the spring and summer.

It attacks the new shoots when the needles are placed, eventually causing the death of these needles and soon of the whole branch.

As the infestation grows, the tree will eventually starve.

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

• Orange-brown spring eggs

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

• In summer, young insects weave a small 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.

• In the fall, during the heat of summer, the woolly aphid goes dormant. They come back and start feeding in the fall and winter.

How to control

woolly aphid

Insecticide. Unfortunately, the only option is an insecticide, and the most effective options are not the most environmentally friendly. So read the application instructions and be careful when treating your trees.

Start by treating the healthiest trees that are the most integrated into your landscaping and the farthest from streams and water sources.

It will take about a month to see a change, and you will need to continue monitoring your trees.

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

Soil treatment. Soil treatment, or soaking the soil, is considered to be the most effective and easiest method of dealing with woolly aphid in domestic landscapes.

1. Look for an insecticide that has the active ingredient imidacloprid. It is sold under various 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 about 3 inches deep.

3. Mix the concentrate according to the instructions on the container and pour it into the trench. The sap of the tree then becomes toxic to the aphid, which drinks hemlock sap for food. Watering the soil can take several months to be effective.

Natural predators. Since large forests obviously cannot be treated with insecticides, researchers are working to develop natural predators to release for large-scale woolly aphid control.

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

The Environment Committee will continue to monitor this concern and provide updates as needed.

Further information is available at, Hemlock Woolly Adelgid: A Threat at University Tennessee Agricultural Extension Publication SP503-G and

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