3958 Bloomington Avenue S. Minneapolis, MN 55407


Tsuga sieboldii

Woolly adelgid

A fully grown adult of the hemlock woolly adelgid is only about the size of a period on this printed page. However, this insect is easily recognized during most of the year by the presence of a dry, white woolly substance on the young twigs. This “wool” is associated with all stages of the adelgid, but it is most abundant and conspicuous during spring when egg masses are present. An egg mass resembles the tip of a cotton swab, although somewhat smaller. Adelges tsugae injures eastern and Carolina hemlock by sucking sap and probably also by injecting a toxic saliva while feeding. This causes the needles on infested branches to desiccate, turn a grayish-green color, and then drop from the tree usually within a few months. Most buds are also killed, so little new growth is produced on infested branches. Dieback of major limbs usually occurs within two years and progresses from the bottom of the tree upwards, even though the infestation may be evenly distributed throughout the tree. Trees often die within four years, but some survive longer in a severely weakened condition with only a sparse amount of foliage at the very top of the crown. These weakened trees are unsightly and have little chance for recovery. They often fall victim to wood-boring insects and diseases and are readily broken and thrown by wind.



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