The spruce bud scale is known to the northeastern United States, among other US locations, and parts of Canada. The mature scales are round, reddish brown in color, and 3 mm wide. Usually, clusters of 3-8 scales are found at the base of new twig growth, and closely resemble buds. There is a single generation per year, with immature spruce bud scales overwintering on the underside of host plant needles. Spruce bud scales remain dormant until spring temperatures warm, sometimes becoming active as soon as late March depending upon the geographic location. By April, once temperatures are warm enough, the female spruce bud scales move to their host plant twigs. In this location, they finish maturing and eggs are retained in the female spruce bud scale body cavity where eventually, crawlers develop. These immature and mobile crawlers appear by approximately the beginning of June and may remain active through July. They then find suitable locations to settle and begin their feeding on the new growth of the plant. During this time, copious amounts of honeydew (sugary liquid excrement) may be excreted. Black sooty mold may grow on top of the honeydew. Additionally, wasps, bees, ants, and other stinging insects may be attracted to the honeydew produced by the spruce bud scale, and may often be noticed before the scales themselves are seen. Spruce bud scales reproduce parthenogenetically (asexually) in North America; however, in other parts of the world reproduction is sexual. The spruce bud scale is non-native in North America, and seems to have originated from Europe.
Found on spruce, the scales are round, reddish-brown and small in size. Usually found at the base of new twig growth and often resemble the new buds. Active in late March through April. Spruce bud scales preferentially infest the lower limbs of their hosts, often in greater numbers, than the upper branches. If the population is high enough, lower host branches may be killed. 4-8 scales feeding in a single location may cause branch shoots to become stunted in size. Weakened trees often support higher populations of the spruce bud scale than healthy trees. The spruce bud scale is capable of producing much honeydew. Black sooty mold may grow on host plant surfaces that are coated in the honeydew.
Visually monitor for spruce bud scales on branch tips near the base of new growth in April, May, and June. Look for young, feeding female scales at first which will appear light brown in color and may be soft to touch. As they develop eggs within their bodies, they may become more plump and firm and turn a dark reddish brown in color. By late June, once the female scales have died, they may become brittle and hollow if dissected with magnification. Use a hand lens to look for migrating crawlers (mobile immatures) from late June through July that will move to the needles where they will settle and feed through September.
If low numbers of spruce bud scales are present on a single planting, branches hosting scales may be pruned out and destroyed to help reduce the population on a single tree before the crawlers emerge. For example, this may be a practical solution on specimen trees with infested lower branches. Prune without disfiguring the host plant.
A variety of natural enemies of the spruce bud scale are known. These include but are not limited to: tiny parasitic wasps (Coccophagus insidiator, Coccophagus lycimnia, Aphycoides clavellatus, and Metaphycus unicolor), ichneumonid wasps (Exochus quadrimaculatus), and predaceous lady beetles (Chilocorus bipustulatus, Exochomus quadripustulatus, Harmonia axyridis, and Scymnus abietis) (ScaleNet).
Abamectin (NL)
Acephate (NL)
Acetamprid (L)
Azadirachtin (NL)
Buprofezin (NL)
Carbaryl (L)
Chlorpyrifos (N)
Clothianidin (NL)
Cyantraniliprole (NL)
Cyfluthrin (NL)
Dinotefuran (NL)
Flonicamid+cyclaniliprole (N)
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)
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.
