The white prunicola scale (Pseudaulacaspis prunicola) is a temperate species of armored scale. It is so very closely related to and easily confused with the white peach scale (P. pentagona) that for a very long time, scientists thought each was a single species. The white prunicola scale and the white peach scale cannot be distinguished from one another in the field. They must be examined beneath a microscope by a skilled armored scale taxonomist. In Massachusetts, of the two species, the scale encountered is most likely to be the white prunicola scale. Adult female scale covers are convex, circular, and white. Male scale covers are smaller, felted, white, and sometimes have a faint median ridge. The body of the adult female is yellow and becomes tinged with pink as she develops eggs. Eggs and first instar nymphs are pink in color (Miller and Davidson, 2005). Typically, the biology of the white prunicola scale occurs two weeks behind (later than) the white peach scale. This delay in their biology occurs throughout the rest of the growing season. Mated adult females are the overwintering life stage. In Maryland, eggs of the white prunicola scale can be found in late April and early May, and again in early July and late August. In northeastern Pennsylvania, egg laying began in mid-May, and again in late-July, with crawlers shortly thereafter. Each female laid approximately 27-78 eggs. In Maryland and points south, there can be 3 generations per year. In points north of Pennsylvania, there are typically 2 generations per year, occurring approximately in early June and early August in central New England.
Trunks and branches primarily of Japanese flowering cherry, lilac, and privet are infested by the white prunicola scale. In New England and Massachusetts, it is more likely that a scale on one of these hosts is the white prunicola scale, than the more tropical and subtropical species known as the white peach scale. The host list of the white prunicola scale is also much smaller, with 18 plant Families and 26 plant genera reported (ScaleNet). This species primarily infests the bark and fruit of its host plants, and is only occasionally found on host plant leaves. Feeding may reduce tree vigor, and foliage may yellow or become sparse. In temperate areas, the white prunicola scale can be a serious pest of Prunus spp. Heavy infestations may cause dieback or mortality of the entire host plant. Management options included here are for ornamental host plants only. If looking for information for fruit-producing trees, visit: https://netreefruit.org/stone-fruit/peaches/insects/white-prunicola-scale-wps .
In heavy infestations, the male covers may be found in white masses on the bottoms of branches that are easily seen if searched for. Crawlers can be monitored for using electrical tape wrapped sticky-side-out on trunks and branches. Search for these armored scales on the bark of host plant trunks and branches.
These armored scales are difficult to manage, especially since they tend to colonize the trunk and larger branches of their host plants. This makes pruning out infested branches very difficult if not impossible. If practical, an attempt can be made to wipe off these scales (using a soft brush) on smaller host plant trunks. This may help with a population of these scales on an individual ornamental planting.
Parasitoids and predators of the white prunicola scale are abundant. Lady beetle predators and wasp parasitoids are important natural enemies of this insect. This includes but is not limited to: the twicestabbed lady beetle (Chilocorus stigma), Lindorus lophanthae, and Exochomus childreni, as well as Prospaltella berlesei, and Aspidiotiphagus citrinus. Predaceous thrips and certain predatory mite species have also been reported as natural enemies of the white prunicola scale (Johnson and Lyon, 1991).
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)
Dormant oil applications may be helpful for managing this pest, approximately in April.
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.