Hemlock Woolly Adelgid

FACTS, IDENTIFICATION & CONTROL

LATIN NAME

Adelges tsugae

APPEARANCE

The hemlock woolly adelgid is tiny – 1.5-mm– and its color varies from dark reddish-brown to dark purplish-black. As it matures, the insect produces a wool-like filament, which acts as a protective coating against any enemies.

BEHAVIOR, DIET & HABITS

The hemlock woolly adelgid has been found in 19 states total: Oregon, California, Virginia, Delaware, Maryland, New York, Pennsylvania, New Jersey, Connecticut, Rhode Island, West Virginia, North Carolina, South Carolina, Georgia, Maine, Vermont, New Hampshire, Tennessee and Kentucky. Other than Oregon and California, it generally has not been known to cause damage to hemlock trees in the western part of the United States.

Hemlock woolly adelgids usually are found near the bark at the base of the needles. They damage host plants by inserting their piercing mouthparts into the base of the plant needles and extracting fluids. This process can significantly weaken the tree’s overall health. 

REPRODUCTION

Overwintering adult females lay eggs in masses during the warmer seasons. The eggs are around 0.25 mm in length and are brownish-orange in color. Depending on the temperature, eggs begin to hatch in April, and hatching is typically completed by late June. The nymphs are reddish-brown and continue to grow in size with feeding. They mature in late September and spend their winters on trees.

SIGNS OF A HEMLOCK WOOLLY ADELGID INFESTATION

Infestations are easily recognizable because of the masses of waxy white filaments that appear at the base of the hemlock. Other signs of an infestation include reduced twig growth, the death of trees or any dieback. 

ADDITIONAL INFORMATION

The best time to attempt to manage this pest is September through October. Any insecticides used during this time frame can be targeted to overwintering females. A spray also can be applied in the summer to reduce the number of nymphs.