Skip to main content

San Jose Scale

San Jose ScaleSan Jose Scale

Hosts:  apple, pear, cherry


Biology:
  San Jose scale is an armored scale that overwinters as a mix of nymphs and adults.  Crawlers (newly hatched nymphs) emerge in late spring and a second generation emerges in late summer.  They feed on sap from leaves, limbs, and fruits. 


Symptoms:
  Feeding on apple and pear fruit appears as red halos with white centers.  Heavy feeding reduces tree vigor and blemishes fruit.


Monitoring:
  Look for limbs encrusted with small, circular, black and gray armored scales.  Monitor for crawlers by wrapping black tape around an infested limb and covering the tape with petroleum jelly; look for trapped crawlers.  There are pheromone traps for male adults but they are mostly unreliable. 


Treatment Threshold:
  Treat at crawler stage if any fruit in the orchard in the prior season had scale.


Degree Day Model:

  • Upper threshold:  90°F
  • Lower threshold:  51°F
  • Crawlers begin hatching approximately 300-400 degree days after codling moth biofix
  • Time to treat is at 600 degree days.


Management Considerations:
Adults are difficult to kill. Dormant oil can kill a portion of overwintering nymphs, but crawlers hatched from overwintering adults will have to be treated when they emerge.