Hemlock Wooly Adelgid

Symptoms: In heavy infestations the feeding damage results in rapid desiccation and discoloration of the foliage. A heavily infested tree may die within four years.

What causes damage: The adelgids over winter as adults. In March and April they begin to lay brownish orange eggs underneath the body of the female which is covered with woolly white wax. The crawlers or immature adelgids are reddish brown and are present throughout the summer. The crawler is the dispersal stage and is spread primarily on the wind. Upon finding a suitable place to feed, the crawlers settle, generally on branch terminals at the bases of needles. As the young adelgids grow, they cover themselves with a white woolly wax. The adelgids are tiny-aphid like insect. It is found primarily on the young branches of hemlock at the bases of the needles. It sucks the sap from the branches and may inject a toxin into the tree during feeding.

What we can do: The hemlock woolly adelgid can be successfully controlled by thorough spraying with a registered insecticide. A dormant rate of horticultural oil may be applied in early March before egg laying begins to kill adult females. The key to control is thorough spray coverage of the tree. Research has shown that excess nitrogen may enhance adelgid populations on hemlock. So it is advisable not to fertilize hemlocks that are infested with the hemlock woolly adelgid.

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