Elongate Hemlock Scale
CTN-037

Prepared by:
Jill Sidebottom, Ph.D.
Area Extension Forestry Specialist, Mountain Conifer IPM
Extension Forestry, College of Natural Resources

November 2009; revised August 2010

Printer Friendly PDF (You will need the free Adobe Reader program to view Adobe PDF formatted publications.

The elongate hemlock scale (Fiorinia externa), is an introduced pest from the Orient. Though commonly associated with hemlocks, EHS can feed on many species of conifers including firs, pines, spruces, cedars, Douglas fir and yews. In western North Carolina, hemlocks and Fraser fir are its most common hosts.

Thought to have been first introduced into the US in New York City in 1908, the scale was slow to spread until the mid-1970s when it greatly expanded its invaded range and is now reported in more than 14 states in the eastern US. First identified in North Carolina at the Biltmore Estate in Asheville in 1992 on Momi fir, the pest was first found on Fraser fir Christmas trees in Yancey County in August 1993. These trees were growing among infested hemlocks and through the 1990s scales were sometimes observed, but were seldom a problem. However, since 2000, the prevalence of this pest has continued to increase until it is now a common problem in many mountain counties. During this same time period, scale numbers were also increasing in hemlocks in the landscape in western North Carolina, in some instances damaging hemlocks before the hemlock woolly adelgid was found.

Effect on the Tree

The EHS is found almost exclusively on the underside of needles. Scales will be found on multiple years of growth. On infested branches, scale numbers average 10 per needle and there can be as many as 30 on a single needle with scales sometimes found on top of each other.

When infestations are heavy, trees may have yellow blotches or patches on the needles and growth will be stunted. However, such symptoms are not commonly seen on Fraser fir in western North Carolina. More commonly what is seen are the white, waxy excretions of the male scales found on the upper surface of needles especially during summer months when males are maturing. Infestations that do not reduce tree growth can still make trees unsaleable because of this white covering to the needles. This pest is also regulated, and trees must be scale-free to ship to other countries or to California.

	Click on photos for larger images.
Figure 1. Occasionally scales will create yellow patches on needles.			Figure 2. The white cotton produced by the males appears on foliage in the summer. Be sure to check for the presence of scales on the underside of needles.

Scale Appearance

The EHS as its name implies is longer than it is wide. The males are white and females brown. Crawlers and immatures are yellow and are not elongated in shape. Crawlers have six legs and two tiny eyes. The female scale is enveloped in a hard covering both above and below. There is only a small, shield-like opening underneath for the feeding tube to be inserted into the needle. Eggs are laid inside this envelope and crawlers, when they hatch, emerge from it.


Figure 3. This adult female has been flipped over to show the shield-like area through which the sscale feeds. Also note the crawler emerging at the far end.	Figure 4. This adult female has been flipped over and teased open to show several eggs.	Figure 5. The waxy covering of the needle can be seen covering this adult female. The yellow portion was the nymphal stage, and the mature scale developed behind it.

Life Cycle

The EHS has two, overlapping generations in the southern Appalachians. Because of this overlap, all life stages can be found almost any time of year, though proportions of one stage to another will vary. Crawlers emerge throughout the growing season and even in winter months, but peak crawler emergence is in May into June and again in late October into November.

The crawlers must find an appropriate feeding site. Crawlers may move somewhere else on the same needle, crawl onto the new growth, or move passively through wind or bird movement onto other trees or fields. Once a feeding site is found they molt, never moving again.

Immature scales appear to burrow under the waxy layer produced by the needle, making them even more protected against pesticide applications and predators. As the scale matures, it forms behind the original yellow immature, making it look as if a smaller scale is attached to a larger. The feeding tube of the immatures is as long as it is, appearing as a tiny coppery wire. The scales feed in epidermal cells.

Immature female scales go through three stages of development while males have additional prepupal and pupal stages. Males emerge as a tiny winged insect with large black eyes and long antennas. Before they emerge, they can sometimes be found under the white cotton of the pupal stage. They have no mouth parts and live only a few days, mating with females. Eggs are produced six to eight weeks after mating. Each female produces 12 to 16 eggs at a time which hatch within a month. Mature females may live for more than one year.

EHS Control

The elongate hemlock scale is difficult to control for several reasons. As an armored scale, it has a hard covering which makes pesticide penetration difficult. Since its life cycle is not synchronous, all life stages are almost always present, meaning that insecticides can not be applied at any given crawler emergence. Since it feeds in epidermal tissue instead of vascular tissue, it is not as easily controlled by systemic insecticides. Also as an introduced pest, it doesn’t have a lot of natural enemies, though there are several that feed on it.

Natural controls. In fact, at one time the EHS was considered to be “self-limiting.” In forest hemlocks, scale numbers seldom increased, primarily because natural controls obtained from the parasitic wasp, Encarsia citrina and potentially other parasitoids. These wasps lay their young in late first or second instars and primarily only in females, where the wasp matures and exits through a hole in the scale. Parasitized scales can be identified by the hole in an otherwise empty scale shell. There are other predators of EHS including various lady beetles, brown lacewings, and dusty wings. In fact, one predator found occasionally in western NC will cover itself with the white waxy cotton produced by the males to hide itself. Pesticide use may increase scale numbers by limiting these natural controls. Though products like Dimethoate and synthetic pyrethroids may kill scales, they may also make them worse because of the effect on natural predators. Therefore, it is important to only use a pesticide when necessary, and to limit the use of these and other broad-spectrum products.

Scouting. Control consists of identifying fields that have scale, then scouting to determine the need for control. Scales are usually found in a field during the summer when the males, and therefore the white cotton they produce, are most common. The white on the foliage may be confused with algae, but if it is EHS, the scales themselves can always be found on the underside of the needles. Lifting up the foliage to look at the back sides of needles is helpful in identifying infested trees. Be sure workers that tag and shear trees are familiar with EHS appearance and will flag infested trees. Scales can also be found when beating the foliage over a pan when scouting for other pests such as twig aphids.

Chemical Treatment

There are currently no treatment thresholds for EHS control. In most fields, scale incidence will continue to increase over time. However, in some instances, scales have caused little trouble. It may be best to assess the amount of visible incidence and damage from the scale over time before attempting controls. Control right before harvesting trees may be necessary to remove the white from foliage. However, if scales are found in a field, shift pest control for other pests to timing and materials that will control scales.

Treating for EHS should be just one part of pest control in Fraser fir. When deciding when and what to treat with, consider other pests that may be present including balsam woolly adelgid, balsam twig aphid and Cinara aphids. Chemicals used for EHS control can make spider mites and especially hemlock rust mites worse. In fields prone to rust mites, time EHS treatment as late in the fall as possible to avoid problems with this pest.

The best time to control scales is in the summer from June through mid-August. Scales can also be controlled before bud break, though typically control would be 5 to 10% better if the trees were treated in the summer. However, if trees are going to be treated in the spring for twig aphids or other pests anyway, there is no reason not to try to control EHS also. If trees are treated before bud break, waiting to as close to bud break as possible will increase efficacy.

Use a high pressure sprayer, creating a fog that moves the materials under the needles. Remember that scales will be on 3 or 4 years of growth, so it is important that all the needles are covered.

The materials that have been most successful to date are Dimethoate (16 oz/100 gallons) + Asana (esfenvalerate) (10 oz/100 gallons). Horticultural oil is a lower toxicity material that consistently gives only 65 to 75% control. If using oil, consider using an encapsulated oil which will cause fewer problems with burn. There are also some indications that Lorsban gives control

.Using Dimethoate + Asana in June, July or August may also give control of twig aphids the following spring. Asana will control balsam woolly adelgid as well. If scales are in a field, consider switching from Thionex or Tastar for adelgid control to Asana + Dimethoate which will provide both scale and adelgid control. Field observations have indicated that fields treated with Asana for adelgid control do not develop the same level of scale incidence as those treated with Thionex.

Safari and horticultural oil can both be used for hemlocks in the landscape for EHS control. Another product labeled for hemlocks in the landscape that appears to control scales well is Distance (pyriproxyfen). Another product that is reported to control scales, but has not always given consistent control in western North Carolina, is Merit (imidaclopprid).

Figure 6. Scales are on 3-4 years of
growth. Insecticide spray must thoroughly
cover the underside of all needles.

Assessing Control

It is not easy to know if scales have been controlled after treatment. Crawlers, nymphs and males are easiest to control. Adult females are the hardest.

A month after application it requires examination under a microscope to determine if individuals are still alive. After several months, visually assessing scale mortality in the field becomes easier as the scales appear dried up though adult females may appear to be dead when they are in fact still alive.

During the next period of fir growth, you can also determine if immature scales are moving onto the new growth. If they are, control was not adequate. In some instances treating two years in a row – in fall and again in the spring – are necessary to get complete control.

Recommendations for the use of agricultural chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by North Carolina Cooperative Extension nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical. For assistance, contact your county Cooperative Extension agent.

Distributed in furtherance of the acts of Congress of May 8 and June 30, 1914. North Carolina State University and North Carolina A&T State University commit themselves to positive action to secure equal opportunity regardless of race, color, creed, national origin, religion, sex, age, or disability. In addition, the two Universities welcome all persons without regard to sexual orientation. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

Jill Sidebottom, PhD
Mountain Horticultural Crops Research & Extension Center
455 Research Drive
Mills River, NC 28759
Phone: 828.684.3562 ~ Fax: 828.684.8715
Email: jill_sidebottom@ncsu.edu

Web Crafter: Anne S. Napier

Updated August 3, 2010

Elongate Hemlock Scale CTN-037