Last week, Cindy Meyer (OSU Extension, Butler County) and I found Cryptomeria Scale (Aspidiotus cryptomeriae) on Canaan fir in a Christmas tree farm in southwest Ohio. The literature indicates this non-native armored scale may be found on the underside of needles on a wide range of conifers including true firs (Abies spp.), Douglas-fir (Pseudotsuga menziensii), hemlocks (Tsuga spp.), spruces (Picea spp.), and perhaps other conifers as well as Taxus (Taxus spp.). However, it appears that cryptomeria scale has a distinct preference for and is most destructive on true firs including Frasier, balsam, and Canaan.
Cryptomeria scale has been a serious problem in tree farms and nurseries in Pennsylvania and several New England states for a number of years and in 2010, two widely spaced infestations were found on Fraser fir in North Carolina. However, Dave Shetlar (OSU Entomology) and I have never found this scale before in Ohio although there have been reports that it may have been spotted in past years on hemlock in eastern Ohio forests.
The literature notes that cryptomeria scale is often misidentified as hemlock elongate scale (Fiorinia externa) (HES). Both scales reside on the underside of needles, have similar life-cycles, and share many conifer hosts including true firs. However, it's important to make a correct identification because cryptomeria is far more damaging on true firs. A close examination with a hand lens or low powered microscope will clearly reveal key identification features between these two armored scales.
HES females are housed under an elongated, opaque, amber to brown waxy covering. You cannot see the females unless you lift up their hard covering. Cryptomeria scales are almost round in appearance. The light yellow females are clearly visible under a light-white, filmy, almost translucent waxy covering. The odd arrangement makes the females look like double rows of fried eggs on the underside of infested needles. Indeed, an alternate common name for this scale is the "fried-egg scale;" it's a great moniker for helping you to remember what to look for!
As with all armored scales, cryptomeria feeds by inserting their long piercing-sucking mouthparts into individual plant cells. According to Richard (Rich) Cowles, (Agricultural Scientist, The Connecticut Agricultural Experiment Station, Valley Laboratory), true firs are particularly sensitive to cryptomeria scale feeding damage with even a small amount of feeding by the nymphs and adults producing highly visible yellow spots and banding on infested needles. Heavy feeding damage will eventually cause needles to turn brown and shed following a pattern of "inside-out" on the branches and "bottom-up" on trees. So, you need to look closely towards the inside of lower branches to detect a developing infestation.
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 cryptomeria scale or other armored scales.
Cryptomeria scale has a life-cycle that is very similar to HES. There are two non-synchronous, overlapping generations per season. What this means is that all developmental stages may be observed throughout much of the growing season. However, there are two times of the year when the highest concentration of the mobile first instar nymphs (crawlers) occur; sometime in late-spring to early-summer and again in late-summer to early-fall. As with other armored scales, the crawlers are the primary target for control.
Rich has shown that a dinotefuran (e.g. Safari) application targeting the first generation crawlers provides exceptional control. This systemic neonicotinoid fits well with an IPM program because it will not affect natural control agents such as the twice-stabbed lady beetle (Chilocorus stigma); a noted scale predator. Indeed, finding this lady beetle provided the first "tip" that I was dealing with a scale insect infestation when I visited the Christmas tree plantation in southwest Ohio. "Rescue" applications of bifenthrin (e.g. Sniper, Talstar) may be used to suppress second generation crawlers; however, multiple applications are required and pyrethroid insecticides are notorious for also suppressing beneficial insects. Clearly, it is best to monitor for this scale starting in early spring so rescue applications are not required.
NOTE: A special thanks to Rich Cowles who generously shared with me by phone and e-mail his considerable experience with the biology, impacts, and management of cryptomeria scale. You can learn first-hand from Rich by viewing his educational videos. Just Google "Richard Cowles Christmas tree armored scale video."