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Plant Answer Line Question

Keywords: Tsuga heterophylla, Trees--Diseases and pests

My Western Hemlock is infested with woolly adelgid. Help! How can I save my tree?


The USDA Forest Service has an entire web site devoted to this pest problem, and includes information on different ways of managing the Hemlock woolly adelgid.

The most effective approach is prevention, as treatment tends to be expensive and is not always effective. Information from University of Maryland Extension does describe the use of dormant oil spray in late winter and summer application of horticultural oil and insecticidal soap, but care must be taken to cover the entire tree. Also, it is important to avoid the use of nitrogen-heavy fertilizers which create a lot of succulent new growth attractive to the pest.

I recommend that you consult a certified arborist for advice on how to save your (Western hemlock). You can obtain referrals from Plant Amnesty or you can select an arborist from the Pacific Northwest Chapter of the International Society of Arboriculture.

Date 2018-04-21
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May 31 2018 13:14:08