I revisited a Cilician fir (Abies cilicica) earlier this week in southwest Ohio that I found to be heavily infested with Elongate Hemlock Scale (EHS) (Fiorinia externa) in 2010. I’ve been monitoring this tree since that time and have watched the scale population rise and fall then rise again; however, the tree has never been treated.
This non-native armored scale is sometimes called “Fiornia scale.” My fir find is a reminder that this non-native armored scale may be found on a wide range of conifer hosts. Beyond its namesake host, EHS will infest firs, Douglas-fir, spruces, cedars, and occasionally pines and yews. However, I’m convinced that all host impacts are not equal.
EHS is native to Japan and was first found in New York, NY, in 1908. Since that time, it has become widespread in Connecticut, Maryland, Massachusetts, New Jersey, New York, Pennsylvania, Rhode Island, and Virginia. Ohio was once considered to be on the western edge of the scale’s spread across the U.S.; however, EHS has now been reported in all areas of the state with the exception of the northwest region.
EHS occurs on the underside of needles and on cones. The common name is descriptive. Mature females are covered by a waxy slightly translucent "test" that is elongated and parallel-sided. The test ranges in color from yellowish-brown to brownish-orange. The waxy tests covering mature males are white and also elongated.
The mobile soft bodied first instar nymphs (crawlers) are lemon yellow. Second instar nymphs (settled crawlers) are also soft bodied; however, they are sedentary and enclosed in an oval, amber-colored covering. The settled crawlers secrete waxy white filaments. Occasionally, the underside of infested needles may become covered by tangled strands of this white flocculent material.
EHS spends the winter as fertilized females or eggs. Overwintered eggs hatch in early spring and overwintered females continue to produce eggs throughout the spring. Thus, the resulting crawler stage lasts for an extended period of time. The crawlers move to new growth where they settle, feed, and eventually develop into mature males and females. The mature scales mate to produce a second generation and eggs produced by the second generation females give rise to individuals that overwinter.
Like all armored scales, the elongate hemlock scale feeds by inserting their piercing-sucking mouthparts into needles to withdraw nutrients from meshophyll cells. Damage symptoms include yellow stippling or banding on the needles, overall needle yellowing, and needle loss. Severe damage can produce branch dieback and heavy infestations may also weaken trees making them more susceptible to other pests or death from environmental challenges such as drought.
Note that unlike "soft scales," armored scales do not suck juices from phloem vessels, so they don't extract large quantities of sugary sap leading to need to exude sugary, sticky "honeydew." Thus, you don't see black sooty molds with EHS or other armored scales.
The Cilician fir I’ve been monitoring has never shown any detectible needle symptoms beyond some minor stippling. Indeed, the tree continues to appear healthy with EHS only revealed by examining the underside of the needles. I have no doubt that EHS can produce severe damage to many of its conifer hosts including other firs; the literature and online photographs clearly show this to be true. Perhaps Cilician fir is capable of dealing with the scale in ways other conifers cannot. Or, other factors may be at work. Research has shown that EHS is “self-regulating” on hemlock with developmental rates, fecundity, and survival declining as populations rise. Regardless, the tree could certainly serves as a “point source” for EHS to spread to other hosts.
Management of this scale is made difficult because all life stages may be present at the same time during the season. Foliar insecticide applications targeting crawlers have been shown to be effective; however, multiple applications are required. Also, foliar insecticide applications may kill bio-allies important in managing this scale such as the lacewing larva I found using its sickle-shaped mandibles to pierce and feed on EHS. The insect growth regulator, buprofezin (e.g. Talus) has been shown to have less of an impact on parasitoid wasps, but may affect other natural enemies.
The systemic insecticide dinotefuran (e.g. Safari) is very effective in suppressing elongate hemlock scale and will have less of an impact on the bio-allies if applied as a trunk application or soil drench. Effective timing includes spring applications before bud-break or shoot elongation and applications made in early fall.