Description of Damage
Immature nymphs and adults damage trees by sucking sap from the twigs.
The tree loses vigor and prematurely drops needles, to the point of defoliation, which may lead to death. If left
uncontrolled, the adelgid can kill a tree in a single year. When not at serious risk to the tree, presence of the
dirty white globular masses of woolly puffs attached to the twigs or base of needles reduces the value of ornamentals.
Identification
These small insects display several different forms during their life history, including
winged and wingless forms. Generally, they are brownish-reddish in color, oval in shape, and about 0.8 mm in length.
Crawler stage nymphs produce white cottony/waxy tufts which cover their bodies and remain in place throughout their
lifetime. The white masses are 3 mm or more in diameter. The presence of these masses on the bark, foliage, and twigs
of hemlock is a sure sign of hemlock woolly adelgid.
Life History
There are four forms of this insect. Each form goes through six life stages (egg, four
nymphal instars, and adult). As a cool weather species, most development of these stages occurs between October and June.
As temperature rises thereafter, the first instar nymphs go into a dormant stage. Eggs are laid by adult adelgids the
following February or March. Half of these eggs develop into a winged, migratory, asexual form that migrate to spruce.
The other eggs develop into wingless adults that remain on the hemlock tree.
Control
Application of insecticides is currently recommended for controlling the hemlock woolly adelgid.
The best compounds are horticultural oils which smother the insects. A one percent solution is recommended from May through
September, and a two percent solution from October to April. Complete coverage of the tree is necessary and can result in 100
percent mortality of the adelgids. Only one complete application of oil is necessary. Soap can also be used, but may be
toxic to the trees. Following treatment, monitor the situation. Tree fertilization can result in more damage, as adelgid
populations are known to flourish on such trees.
All-Seasons Spray Oil
Read The Label And Follow Instructions for Safety And Desired Results
Label
Further Reading
Johnson, W.T. and H.H. Lyon. 1991. Insects That Feed on Trees and Shrubs. Cornell Univ. Press, N.Y. 560 pp.
McClure, M.S. 1989. Evidence of a polymorphic life cycle in the hemlock woolly adelgid, Adelges tsugae (Homoptera: Adelgidae). Annals Entomological Society of America 82:50- 54.
Prepared by S.M. Salom, Department of Entomology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0319.
Visit Virginia Cooperative Extension
Photo of HWA infested branch.Third Symposium on Hemlock Woolly Adelgid in the Eastern United States.
