San Jose Scale

Hosts

Apple, pear, cherry, peach, nectarine

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/Damage

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 have not been reliable in Utah. 

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.