The hemlock woolly adelgid (HWA) is a serious pest of Canadian hemlock, Tsuga canadensis, in the northeastern states. This insect was discovered in Connecticut in 1985 and has spread rapidly to both cultivated and forest hemlocks.

Adelgids are small, soft-bodied insects that are closely related to aphids. They have piercing-sucking mouthparts, which are inserted to remove plant sap for food. The HWA feeds primarily on young branches causing cessation of tree growth, discoloration and premature drop of needles, dieback of branches and possible death of the tree in as little as one year.

Description and Life History
The females are oval, blackish-gray, about 2mm in length and serve as the over-wintering stage. The brownish-orange, very small, oblong eggs are laid in cottony white egg sacs (about 50 eggs per sac) on young twigs from late March to May. The presence of the egg sacs offers the most visible diagnostic evidence of a HWA infection. The eggs hatch into reddish-brown crawlers (nymphs) from early April through early June and begin feeding on the sap of young twigs, maturing into adults in a few weeks. Some of the adults are wingless and remain on hemlock for a second generation, while the winged forms may fly to nearby hemlocks or spruces.

None of the common native and exotic spruces appear to be suitable for the winged HWA to complete its life cycle. Second generation crawlers initially feed on new twigs during July but become dormant in late summer through early autumn. Crawlers resume feeding in mid-October and develop into the over-wintering adults. They feed all winter and mature by spring.

Pest Management and Control
Infestations of the HWA can be detected early by periodically examining young twigs for the presence of the egg sacs. They are readily observed in the spring before the eggs have hatched. Keep in mind that remnants of old egg sacs may remain on twigs long after the eggs have hatched and the insect has been controlled. Early detection is very important because injury to hemlock may develop quickly. That is why periodic examinations are an important practice in the control of the HWA.

Several insecticides are available that will provide excellent HWA control; however, insecticides should not be applied on a preventive basis. Many of the hemlocks in Connecticut will not be infested and will not need treating. Controls should be applied only when HWA infestations are observed.

An excellent time to control HWA infestation is from July through September after the eggs have hatched and the young adelgids are relatively unprotected. Summer oil and insecticidal soap have been found to provide excellent control with one application, provided complete coverage is made in this time period. Both insecticides kill only by direct control. Thorough coverage with a drenching spray is essential for control. Dormant oil is effective for HWA control when applied in April to mid-May. It will also control scale insects and mites at the same time.
Unfortunately, natural enemies, such as diseases, parasites and predators, have not been numerous enough to achieve significant management, but they may offer hope in the future.

For pesticide recommendations call the UConn Home and Garden Education Center at 877-486-6271.

The information in this material is for educational purposes. The recommendations contained are based on the best available knowledge at the time of printing. Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended. The Cooperative Extension system does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others which also may be available.All agrochemicals/pesticides listed are registered for suggested uses in accordance with federal and Connecticut state laws and regulations as of the date of printing. If the information does not agree with current labeling, follow the label instructions. The label is the law.Warning! Agrochemicals/pesticides are dangerous. Read and follow all instructions and safety precautions on labels. Carefully handle and store agrochemicals/pesticides in originally labeled containers immediately in a safe manner and place. Contact the Connecticut Department of Environmental Protection for current regulations.The user of this information assumes all risks for personal injury or property damage.Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Kirklyn M. Kerr, Director, Cooperative Extension System, The University of Connecticut, Storrs. The Connecticut Cooperative Extension System offers its programs to persons regardless of race, color, national origin, sex, age or disability and is an equal opportunity employer.