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Elongate hemlock scale, sometimes known as the fiorinia scale, is a serious armored scale insect pest of hemlock, Tsuga spp., on ornamental and forest trees in Newyork.
Elongate Hemlock Scale
Elongate Hemlock Scale less preferred host plants, if infested, are usually growing adjacent to infested hemlocks. The scale insect was unintentionally introduced into the United States from Japan. It was first observed in Queens. This pest occurs in Connecticut, Maryland, Massachusetts, New Jersey, New York, Ohio, Rhode Island, and Virginia.
The waxy covers of this species can be observed on the lower needle surface as well as on new cones. The flattened, elongate, light yellow brown to brownish orange waxy cover of the adult female is about 1.5 mm long. The adult femaleâ€™s body beneath the waxy cover, eggs, and crawler stage are yellow. The white, waxy cover of the male is smaller. When closely examining infested hemlock needles, adult males may look like tiny wasp parasitoids as they crawl across the needles.
Adult male scales only have one pair of wings. Sometimes waxy secretions from settled crawlers may build into a mass of tangled strands. These waxy strands may be so abundant that it gives the lower surface of infested needles a white appearance. When this condition is present, it may cause uninformed individuals to misdiagnose this as hemlock woolly adelgid.
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.
Damage:Scales injure host plants by inserting their threadlike, piercing-sucking mouthparts into needles and withdraw vital nutrients necessary for plant growth from mesophyll cells. Armored scale insects do not feed on the contents of vascular cells. Excessive loss of plant fluid reduces the growth and health of the plant. Feeding injury causes needles to develop yellow banding on the top of infested needles. This injury causes needles to drop prematurely giving the crown of an infested tree a thin appearance. Frequently, this key pest is found on the same hemlock tree with hemlock woolly adelgid, Adelges tsugae . There are several key insect and mite pest species that feed on hemlock foliage. Itâ€™s important to accurately identify what pest species or causal organism is present when maintaining the health of hemlocks. An infestation of this armored scale weakens trees allowing successful attack by secondary organisms such as the hemlock borer, Melanophila fulvoguttata , or Armillaria root rot.
Elongate Hemlock Scale
Control:In fact, at one time the EHS was considered to be â€śself-limiting.â€ť 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.
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.
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