Green Tech Tree

Insects Control & Tree Diseases

Wooley Hemlock Adelgid

tree care insect control Hemlock woolly adelgid (Adelges tsugae), commonly abbreviated as HWA, is a true bug native to East Asia that feeds by sucking sap from hemlock trees (Tsuga spp.). In eastern North America, it is a destructive pest that poses a major threat to the eastern hemlock (Tsuga canadensis) and the Carolina hemlock (Tsuga caroliniana). The range of Eastern Hemlock extends north of the current range of the adelgid, but there are fears that the adelgid could spread to infect to these northern areas too.

Accidentally introduced to North America from Asia in 1924, HWA was first found in the eastern United States some decades later. In Pennsylvania, for example, the earliest record is from 1967.[1] The pest has now been established in eleven eastern states from Georgia to Massachusetts, causing widespread mortality of hemlock trees. 50% of the geographic range of eastern hemlock has been impacted by HWA.

The presence of HWA can be identified by its egg sacs, which resemble small tufts of cotton clinging to the underside of hemlock branches. Hemlocks stricken by HWA also tend to have a grayish-green appearance, whereas healthy hemlocks are dark green. Hemlock woolly adelgid reproduces asexually and can have two generations per year. Between 100 and 300 eggs are laid in the woolly egg sacs beneath the branches. Larvae emerge in spring and can spread on their own or with the assistance of wind, birds and/or mammals. In the nymph stage, the adelgid is immobile and settles on a single tree. The next stage is the adult, which needs a species of spruce not found in the Eastern United States to sexually reproduce, so the only populations from year to year are the two asexually produced generations.

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