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.