Hemlock Woolly Adelgid

Community, Lifestyle
Hemlock Woolly Adelgid

Have you seen small white cottony balls on hemlock trees? If you have then that means those trees are infested with Hemlock woolly adelgid (HWA). Let’s look at why it’s important to preserve hemlocks, what is the pest that is killing them, and what you can do to save them. We are getting to the time of year when they really start to come out.

Hemlocks are a native species that ranges from Maine to Northern Alabama. They are a keystone species that provides habitat for about 120 species of vertebrates and over 90 species of birds. Hemlocks are unique in their ability to thrive in shade. This attribute makes them common in ravines and along rivers and streams. Their proximity to streams and rivers means that they are crucial in reducing erosion and watershed protection. Hemlocks can be identified by their needles. They have short flat needles with two distinctive pale white stripes on the underside. The needles are wider at the base and taper to a rounded tip, unlike firs that have parallel sides the whole way down.

HWA is a very small insect. The white cottony sacks on the hemlock trees are egg sacks of HWA. They are an invasive species from Asia that doesn’t have a natural predator here. HWA feeds on the sap inside of hemlock trees. Wind, birds, deer, or humans can spread the HWA. Once a tree has become infected, it will die within four to 10 years. Therefore, it is important to treat trees as soon as possible after finding that they have been infected.

It is important to treat your own trees with cultural and chemical controls. Cultural controls include keeping hemlocks well mulched and watered. Hemlock trees don’t have very deep roots and droughts can make them more susceptible to infection. Don’t place any bird feeders or deer feeders near your trees. Birds and deer can carry the eggs for long distances. If you are hiking in an area that has HWA wash your clothes afterward because you may be carrying eggs. Be careful to not over-fertilize your trees as that could make them more enticing to HWA. Cultural controls may keep your trees healthy, but when they become infested, chemical controls are the only option. Chemical controls involves treating your tree with either Imidacloprid or Dinotefuran, and is the most common and effective method of control. An imidacloprid treatment will last four or five years. However, it may take one year before it is effective. Dinotefuran will last for two years in the tree and will take about four to six weeks to take effect. The ideal way to apply either of these insecticides is by soil injection or soil drench. Putting the insecticide in the soil will mean quicker uptake by the plant and reduce the chance of off target drift. If the trees are near open water, a trunk injection of insecticide is necessary, which will require a professional. Whenever applying a pesticide it is important to familiarize yourself with the label before using the product. 

The Union and Towns County Extension Offices each have a soil injector that is available to be checked out. Checking it out requires a $250 dollar deposit that will be returned when the injector is brought back. I also have a soil drench kit in each office, which are simpler to use, especially if you don’t have many trees. You must provide your own insecticide.

Contact your local Extension Office or send me an email at [email protected] if you have any questions about HWA.

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