Hemlock woolly adelgid is an aphid-like insect that attacks and kills hemlock trees. Its egg sacs, which look like cotton balls or clumps of snow, can be found at the base of needles.
The environmentally safest chemical control methods for treating individual trees are nontoxic insecticidal soap and horticultural oil. These are sprayed on the foliage and smother the insects as they dry. Most trees need to be treated on a yearly basis.
What homeowners can do to control Hemlock Woolly adelgid
You can apply horticultural soaps and oils 2-4 times per year in an effort to control the population to a point where the insect is not harming the tree. However, even with control there will still be active scale populations on the tree that will still cause sap to drip, and attract wasps, etc. The insect is protected by a hard shell that pesticides will not penetrate. The only time to spray is in the spring or late summer/fall when the new crawlers (young nymphs) are mobile. When the insect cannot be treated, the only options are to prune the tree to reduce the problem, or prune away from a used area such as a deck.
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