- San Jose scale (Quadraspidiotus perniciosus) is a non-native type of armored scale insect and can be difficult to manage as their waxy body covering shields them from predators and certain pesticides. Learn more about scale insect groups and biology on Introduction to Scale Insects.
- This is a common pest of fruit trees and can cause plant decline and dieback when populations are high. This scale species has a very wide host plant range.
- Target monitoring and control efforts to the vulnerable crawler stage. Learn more about what to look for on Monitoring for Scale.
- Mature female covers are circular, with concentric rings of gray to brown with a yellow center, and up to 1/16” (1.5 mm) in diameter.
- Male covers are elongate to oval, similar in color and pattern, and slightly smaller.
- Crawlers are yellow.
Common host plants
Plants in the rose family (a large group, with many popular species) are preferred. Overall, species in 81 plant families can be utilized by this scale.
- Fruit trees, with apple (Malus domestica) and pear (Pyrus) being more severely damaged. Even so, it remains a serious pest on sweet cherry (Prunus avium), peach (Prunus persica), prune-type plums (Prunus domestica), and other tree fruits.
- Nut trees and several fruiting shrubs (edible berries).
- An array of large-statured shade trees, smaller-statured flowering trees, and ornamental shrubs, including flowering plum (Prunus cerasifera), crabapple (Malus), rose (Rosa), and cotoneaster (Cotoneaster).
Where to look
- They will be found year-round on the bark of branches of all sizes.
- They can also be found on the skin of fruits and occasionally on foliage.