San José scale

San José scale (Comstockaspis perniciosa) is a polyphagous pest of deciduous fruit trees including apple, pear, peach, plum, currants; nut-bearing trees and some woody ornamentals. Comstockaspis perniciosa originated in Eastern Asia and has a global distribution due to accidental introductions. The lifecycle is completed in approximately 30 days, with development from two nymph stages, with the first instar referred to as crawlers, to prepupal (male only), pupa (male only) and adult. There can be one to five generations per year depending on location.  Adult scales are small (1-2mm) and are yellow or orange and dark gray in color.

Adults and nymphs feed on the bark of the tree and sometimes on the fruit. Damage symptoms can appear as discoloration on leaves and bark, dieback, lesions and growth inhibition. Crop loss is difficult to assess but overall, trees lose vigor and have a shorter lifespan.  Red spots on fruit are another sign of damage.

Once populations are established, San José scale can be difficult and expensive to control.  This is mostly due to the biology of the pest.  Treatment methods can range from fumigation of seedlings, foliar sprays of horticultural oil to smother overwintering stages and insecticides for the crawler stage.  Systemic insecticides can be used foliarly or applied at the base of the plant in the root zone.  While most insecticides are effective and have not shown cross resistance, resistance to some products exists.

There is no listed IRAC susceptibility test method available for scales

SYNONYMS

Aonidiella perniciosa
Aspidiotus perniciosus
Diaspidiotus perniciosus
Quadraspidiotus perniciosus

EPPO Code: QUADPE

resistance profile

The first documented case of resistance to insecticides was reported in populations of Comstockaspis perniciosa in 1914. More recently, resistance has developed to organophosphates.