Gymnosporangium juniperi-virginianae
Fungal disease requiring two hosts: junipers/cedars and apples/crabapples. Causes orange spots on apple leaves and fruit.
Bright orange-yellow spots on apple leaves. Orange, tube-like structures on leaf undersides. Distorted fruit with orange lesions. Galls on cedar/juniper.
Rust fungus that alternates between juniper/cedar (winter host) and apple/crabapple (summer host).
Spores from cedar galls infect apples in spring. Spores from apple leaves infect cedars in summer. Wind-borne over long distances.
Wet spring weather during apple bloom. Proximity to infected cedars/junipers. Susceptible apple varieties.
Plant resistant apple varieties. Remove cedars within 1-2 miles if practical. Remove galls from cedars in late winter.