Dynaspidiotus (formerly Nuculaspis) tsugae is also known as the shortneedle evergreen scale or the shortneedle conifer scale. It is a non-native armored scale insect that was first noticed in New Jersey on Tsuga diversifolia and T. sieboldii shipments from Japan in 1910. It has since been reported from Connecticut, Maryland, New York, and Rhode Island (Johnson and Lyon, 1991; Miller and Davidson, 2005). A sample of Picea glauca (white spruce) submitted to the UMass Plant Diagnostics Laboratory in November of 2017 from Barnstable County, Massachusetts was confirmed to contain Dynaspidiotus tsugae (Simisky, initial identification; confirmed molecularly and morphologically by the Normark Lab at the University of Massachusetts, Amherst, personal communication).
The shortneedle evergreen scale is typically found on the underside of the host plant needle, but if the population is high enough, the needles may be nearly completely coated with scales. Two generations of the insect have been typically reported in Connecticut per year. Second instar nymphs (immature stages) overwinter and crawlers (an immature but mobile form of the insect) are present from late May to early July as reported from Connecticut. Adults of this species have been reported in April (Johnson and Lyon, 1991). The first generation of eggs may be found beneath the hardened covering of the female by early May. The second generation of eggs can be found in early August and a second generation of crawlers is present from early August to early November in CT (McClure, 1978). 5 developmental stages have been reported for the males of this species and 3 for the females. May be confused for Hemiberlesia (formerly Abgrallaspis) ithacae or the hemlock scale.
The shortneedle evergreen scale has been particularly problematic in hemlock trees in CT in the past (Mark McClure, 1987). Leaf yellowing and premature needle drop, sometimes killing trees, can occur. In Japan, trees under stress due to poor growing conditions are most impacted. In CT, this scale insect has historically been a severe pest of native hemlock, however Japanese species of hemlock tend to have higher populations of the scale. The damage this insect causes is through its feeding, using piercing-sucking mouth parts to drain host plant fluids. On native hemlock, McClure, 1980a, found that the elongate hemlock scale (Fiorinia externa) may outcompete the shortneedle evergreen scale. Damage to spruce in Rhode Island has also been reported.
The shortneedle evergreen scale may preferentially colonize the young needles of the lower crown of its host plants first, so prioritize initial visual monitoring efforts in these areas. This species may not be noticed until the host plant develops symptoms of leaf yellowing or premature needle drop. Monitor the lower needle surface with magnification, however, in high populations scales may be seen on all sides of the needle.
Such options are limited for this species as these insects tightly adhere to the host plant needles and cannot typically be sprayed off the plant with a strong stream of water, as may be the case with some other Hemiptera. If the infestation is caught early, and the scales are not present throughout the entire host plant (but perhaps on one or few localized branches), infested branches may be cut and removed if this action does not disfigure or reduce the overall health of the plant. Any removed branches should be burned if safe or possible to do so. Do not throw in a compost/yard waste area near susceptible hosts. Avoid nitrogen fertilization of infested host plants. McClure, 1988 reports that in infested hemlock trees, nitrogen fertilization increased the population size of the scale insects.
An encyrtid wasp parasite, Aspidiotiphagus citrinus, exists in CT and likely other areas where this scale has been introduced, but Johnson and Lyon note that on ornamentals, this wasp rarely is present in sufficient numbers to keep the scale population low enough. Other natural enemies reported for this pest include a certain parasitic wasp in the family Aphelinidae, 3 other encyrtid wasp parasitoid species, and possibly others. Any chemical management options, if employed, should seek to preserve the populations of these natural enemies. Be aware that certain active ingredients do not only kill the pest insect in question, but are also harmful (and possibly lethal) to natural enemies also present.
Abamectin (NL)
Acephate (NL)
Acetamprid (L)
Azadirachtin (NL)
Buprofezin (NL)
Carbaryl (L)
Chlorpyrifos (N)
Clothianidin (NL)
Cyantraniliprole (NL)
Cyfluthrin (NL)
Dinotefuran (NL)
Gamma-cyhalothrin (L)
Horticultural oil (L)
Imidacloprid (L)
Insecticidal soap (NL)
Lambda-cyhalothrin (L)
Neem oil (NL)
Pyrethrin + sulfur (NL)
Pyriproxyfen (L)
Spinetoram + sulfoxaflor (N)
Chemical management of this species (as with many other armored scale insects) is difficult in terms of timing of the application. Because the insects are usually protected by a waxy coating (test), they can be missed by active ingredients in insecticides that require contact with the organism to be effective. Targeting the mobile stage of the insect (the immature crawlers) is helpful as these insects are the most vulnerable life stage. Late June-early July has been reported from CT (McClure, 1987) to be the best time to target the crawler stage of this insect, however crawlers may be active over a period of weeks, and peek crawler activity varies with site location and is difficult to predict. Dormant oil applications (according to label instructions to avoid host plant injury at certain temperatures for certain hosts) have been shown to be effective for decreasing populations of this insect by McClure, 1987. Applications were made in that experiment in CT in April (a single application at each experimental location). Some professionals report varying success with dormant oil applications, historically, for this pest.
Active ingredients that may be applied systemically include: abamectin (injection), acephate (injection), acetamprid (injection), azadirachtin (injection, soil drench), clothianidin (soil drench), cyantraniliprole (soil drench, soil injection), dinotefuran (soil drench), imidacloprid (soil drench), and neem oil (soil drench).
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.
