The obscure scale is the most common economically significant species of scale in this genus on oaks. However, other closely related Melanaspis species, such as M. tenebricosa, or the gloomy scale can be confused for this species in the field. The adult female cover (test) of the obscure scale is flat, circular, and gray in color, but shiny black when rubbed. The male cover is similar in color and texture to that of the female, but elongated in shape. Males and females mate in late May to early June. Most of the eggs are reported in July. Newly hatched crawlers emerge shortly after and can be found on infested stems and branches for a long period of time, anywhere between mid-July through September. The body of the adult female, eggs, and crawlers are all light pink or purple in color. The first batch of crawlers will often settle under the covering of dead scales, while crawlers that hatch later in the season will move to uninfested branch and stem parts to feed. To complicate the life cycle further, observations have indicated that crawlers appear on white oaks in August whereas they are observed in July on red oaks (this may indicate there are two sibling species - species identical in appearance, but reproductively isolated). By October, second instars are present and this is the life stage that overwinters (both males and females). One generation per year is documented.
Like all scales, the obscure scale removes host plant fluids through its piercing and sucking mouth parts. Severe infestations can lead to wilting and premature leaf drop. In combination with other stresses, branch dieback can occur. Branches and stems may appear deformed in severe infestations where scales are layered on top of one another after many seasons of activity. (Dead scales can remain attached to the host plant, and may be heavily encrusted on the bark.) Quercus, Ulmus, and Carya spp. are preferred hosts of this insect. While records exist of the obscure scale on the other hosts listed here, Miller and Davidson (2005) note that they could be misidentifications of another closely related Melanaspis species from southern states (M. nigropunctata). The obscure scale may be one of the most damaging insect pests of shade trees in certain parts of the eastern United States. Pin oak and willow oak are some of the most susceptible hosts.
Monitor susceptible host plant branches for overwintering second instar nymphs on branches and stems. Because the scale coverings, even of dead scales, cling to the host plant bark, heavy infestations that have been present for multiple years may be detected any time of the year if the layered, encrusted scales are searched for. Take note if branches appear deformed or lumpy/misshapen. The exact timing of crawler emergence and targeting that life stage is particularly difficult for this armored scale insect.
Reduce host plant stress from other stressors, as this can help them withstand scale infestations. Practices to promote host plant health will help reduce the impact of obscure scale infestations. Plant the right plant for the right site, as poor site conditions can also predispose trees to difficulty with scale infestations.
The obscure scale may be abundant on landscape and park specimen oaks despite relatively high parasitism rates in these locations, while it is typically not a notable problem on forested oaks. A parasitic wasp, Encarsia aurantii, was released as a biological control organism to reduce obscure scale populations. An introduced lady beetle predator, Chilocorus kuwanae, may also feed upon the obscure scale. Additional natural enemies recorded from obscure scale populations include but are not limited to: Ablerus clisiocampae, Coccobius varicornis, Coccophagoides fuscipennis, Encarsia berlesei, and Thysanus ater. Additionally, fungi including Nectria aurantiicola and Nectria flammea have been reported to infect obscure scales (ScaleNet).
Abamectin (NL)
Acephate (NL)
Acetamiprid (L)
Azadirachtin (NL)
Buprofezin (NL)
Carbaryl (L)
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)
The obscure scale is difficult to manage for several reasons. First, egg laying and crawler development occurs over the course of several weeks, making treatment difficult to time. Second, the crawlers establish under the waxy, protective covering of dead scales, protecting them from parasitism and contact insecticides before they mature and produce their own protective covering or test. Miller and Davidson (2005) note that dormant oil applications on oak are an effective means of managing this insect. Consider that there are natural enemies of the obscure scale when selecting chemical management options - reduced risk insecticides will lower the chances of unintended consequences for these natural enemies.
Active ingredients that may be applied systemically include: abamectin (injection), acephate (injection), acetamiprid (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.
