The Real Christmas Tree Board (RCTB), in conjunction with Michigan State University Extension, recently hosted a presentation addressing elongate hemlock scale (EHS).

EHS, also known as the fiorinia scale, is a serious armored scale insect pest known to infest ornamental and forest trees such as Canaan and Fraser fir and other Eastern hemlock trees. It is among the most pressing pest concerns faced by Christmas tree growers in Connecticut, Maryland, Massachusetts, New Jersey, New York, Ohio, Rhode Island and Virginia.

“EHS decreases the aesthetic value of Christmas trees, for which they are popular,” said Dr. S. Priya Rajarapu, a biochemist and molecular biologist at North Carolina State University. “The female insects feed on the underside of the needles which causes this mottling effect, which results in a yellowish mosaic appearance of the needles. Not only that, the male insects form these white cotton-like discharges on the Christmas trees, which also decreases their aesthetic value.”

The adult EHS female’s body beneath its waxy cover, eggs and crawler stage is yellow. The white, waxy cover of the male is smaller. When closely scouting for the pest, adult EHS males may look like tiny wasp parasitoids as they crawl across the needles. Adult male scales only have one pair of wings.

The females deposit eggs beneath their waxy covers in early spring and may continue to lay eggs through early summer. A single female may produce up to 20 eggs in her lifetime. In three to four weeks, eggs hatch into first instar nymphs called crawlers that migrate to new needles on the same plant.

Elongate hemlock scale infestation on hemlock. Photo courtesy of Eric R. Day/Virginia Polytechnic Institute,

Rajarapu explained that outbreaks of EHS have been contained to the Northeastern and Mid-Atlantic regions of the U.S. Consequently, she is researching methods to best prevent the affliction from spreading to the Western U.S. and the American South. She pointed to the shipping of Fraser firs grown in North Carolina to buyers in Wisconsin, Washington State and Florida.

While EHS does not normally cause excessive damage to Fraser firs, those trees can serve as carriers and provide a means of transport, allowing this insect to spread to new regions and more susceptible conifer varieties.

Rajarapu discussed a number of control methods Christmas tree growers can use to contain any outbreaks of EHS.

• Cultural Control – Trimming the branches of a tree with heavy infestations of EHS can prevent population growth from the very beginning and prevent the spread to healthy trees in its immediate vicinity.

Rajarapu added, “Spacing the trees out while planting can help prevent spreading, as EHS is largely moved from tree to tree by the wind.”

• Natural Control – The insect populations can be controlled by parasitoids, tiny wasp-like creatures that lay eggs inside other insects. Unlike parasites, parasitoids eventually kill the host they feed on.

According to Rajarapu, “Encarsia citrina is a generalist parasitoid which is very effective at feeding on and destroying EHS. Lady beetles are another voracious natural predator of EHS.”

• Chemical Control – Neonicotinoids are a class of insecticides chemically related to nicotine. Rajarapu pointed to the neonicotinoid Safari as being particularly efficient, producing consistent results in controlling EHS populations in the field.

“Safari consistently eradicates over 90% of EHS infestations when applied in the field,” she noted.

For more information visit

by Enrico Villamaino