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Comstockaspis perniciosa (Formerly Quadraspidiotus perniciosus)

San José scale on Cydonia oblonga. Photo: John A. Davidson, Univ. Md, College Pk, Bugwood.
Scientific Name: 
Comstockaspis perniciosa (Formerly Quadraspidiotus perniciosus)
Common Name: 
San José Scale
Growing Degree Days (GDD's): 
None available at this time.
Host Plant(s) Common Name (Scientific Name): 
Apple (Malus spp.)
Boxwood (Buxus spp.) *Population usually small on this host. (Johnson and Lyon, 1991)
Cotoneaster (Cotoneaster spp.) *Very susceptible to damage. (Johnson and Lyon, 1991)
Crabapple (Malus spp.)
Dogwood (Cornus spp.) *Population usually small on this host. (Johnson and Lyon, 1991)
Firethorn (Pyracantha spp.) *Very susceptible to damage. (Johnson and Lyon, 1991)
Hawthorn (Crataegus spp.) *Population usually small on this host. (Johnson and Lyon, 1991)
Linden (Tilia spp.) *Population usually small on this host. (Johnson and Lyon, 1991)
Mountain ash (Sorbus spp.) *Population usually small on this host. (Johnson and Lyon, 1991)
Privet (Ligustrum spp.) *Population usually small on this host. (Johnson and Lyon, 1991)
Rose (Rosa spp.) *Population usually small on this host. (Johnson and Lyon, 1991)
Walnut (Juglans spp.) *Population usually small on this host. (Johnson and Lyon, 1991)
Insect Description: 

The San José scale was first described in North America and is still common throughout much of the United States and Canada, however, this insect originated in Asia. It was first reported in the United States in 1810 on a shipment of ornamental plants. The overwintering life stages of the San José scale may be partially grown males and females that will continue to mature as temperatures warm in the spring. Males emerge and mate at the time of petal fall. Eggs develop and hatch within the body of the female. Each female may produce approximately 400 lemon-yellow, tiny young. Immature San José scales (crawlers) mature rapidly, and depending upon climatic conditions and geographic location, as many as 5 overlapping generations have been reported in a single season. In the Northeast, this overlapping of generations may occur from mid-May through September, with crawlers active in early to midsummer. In more northerly locations, there may only be 2-3 generations per year. Depending upon the source, some also note on average 3-3.5 generations occuring per year. Males may take approximately 25 days to mature, and females may take approximately 31 days to mature. The entire life cycle may be completed in approximately 37 days. Settled scales create a gray-yellow, circular covering that darkens in color as they age with a black spot in the center. On apple and pear hosts, a symbiosis of this scale and at least two species of Septobasidium fungi have been observed in research conducted in Turkey. Crawlers of the San José scale have been observed to disperse phoretically - that is - by attaching themselves to other insects that can fly them to a new host. This includes using the housefly (Musca domestica), mealybug destroyer lady beetles (Cryptolaemus montrouzieri), and the Argentine ant (Linepithema humile) to move to a new location (Magsig-Castillo et al., 2010).

Damage to Host: 

Damage is caused to the host plant when immatures and female scales feed on host plant fluids with piercing-sucking mouthparts. The tissue around feeding scales may turn red in color, and on twigs or small branches this color can extend into the inner bark and even xylem. This feeding slowly causes the death of twigs and branches, and in heavy populations may lead to the death of the plant. Twigs of many fruit trees and ornamentals may be impacted by this insect - well over 60 different fruit and ornamental trees (at least 79 genera in 42 families are reported by ScaleNet). All parts of the host plant except the roots may be fed upon by the San José scale, with the twigs and small branches favored. If the population of scale is heavy, the buildup of their covers (tests) may form a gray "crust" in these areas. San José scales may be found on fruit, such as apples.


Female San José scales produce a sex pheromone that is now commercially available and can be used to trap males. Hang traps in trees where San José scale populations are suspected. Monitor traps weekly. Crawlers can also be monitored for during the growing season by wrapping twigs with black electrical tape, sticky-side facing out. Monitoring for the timing of crawler emergence can be used to plan chemical management applications. During the dormant season, twigs and small branches can be visually monitored for overwintering life stages or the buildup of scale coverings.

Cultural Management: 

Prune out and destroy heavily infested branches, if possible without disfiguring or further harming the host. 

Natural Enemies & Biological Control: 

Natural enemies of the San José scale are known, including Ablerus, Apanteles, AphytisArchenomus, Coccobius, and Encarsia spp. parasitoid wasps. If choosing a chemical management option to reduce a population of San José scale on an individual host plant, choose a reduced risk option to help preserve natural enemies. Predators including lacewings, lady beetles, and many others are also reported. ScaleNet reports natural enemies of the San José scale in 59 genera in 22 families in the literature. Research has shown that formulations of entomopathogenic fungi are effective at killing San José scales. These include Beauveria bassiana and Lecanicillium lecanii.

Chemical Management: 

Abamectin (NL)

Acephate (NL)

Acetamprid (L)

Azadirachtin (NL)

Bifenthrin (NL)

Buprofezin (NL)

Carbaryl (L)

Chlorpyrifos (N)

Chromobacterium subtsugae (NL)

Clothianidin (NL)

Cyantraniliprole (NL)

Cyfluthrin (NL)

Dinotefuran (NL)

Fenpropathrin (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)


High efficacy (93% mortality of San José scale nymph) was shown for 6% soybean oil and 3% petroleum oil applied in the dormant season (Hix et al., 1999). 

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.

Read and follow all label instructions for safety and proper use. If this guide contradicts language on the label, follow the most up-to-date instructions on the product label. Always confirm that the site you wish to treat and the pest you wish to manage are on the label before using any pesticide. Read the full disclaimer. Active ingredients labeled "L" indicate some products containing the active ingredient are labeled for landscape uses on trees or shrubs. Active ingredients labeled "N" indicate some products containing the active ingredient are labeled for use in nurseries. Always confirm allowable uses on product labels. This active ingredient list is based on what was registered for use in Massachusetts at the time of publication. This information changes rapidly and may not be up to date. If you are viewing this information from another state, check with your local Extension Service and State Pesticide Program for local uses and regulations. Active ingredient lists were last updated: January 2024. To check current product registrations in Massachusetts, please visit: .