Cedar apple rust
A fungal disease that alternates between juniper or red cedar and apple trees, causing bright orange spots on apple leaves and fruit.
Also known as: Gymnosporangium rust
Symptoms and identification
Bright yellow-orange spots with red borders appear on apple and crabapple leaves in late spring, and tiny tube-like growths form under them. Leaves and fruit may drop early. On junipers, brown woody galls appear that sprout bright orange gelatinous horns in wet spring weather.
Causes
The fungus needs both hosts to complete its life cycle. Spores from juniper galls in spring rain blow to nearby apple trees, and spores from apples later reinfect junipers. It is most common where junipers grow within a few hundred metres of apples.
Organic treatment
Remove and bin galls from junipers before spring rains. Pick up affected apple leaves in autumn. Sulphur or copper sprays at bud break may reduce infection.
Prevention
Plant resistant apple varieties, avoid growing apples and junipers close together and remove galls from junipers in late winter. Prune apple trees for good airflow.
Chemical treatment (use with care)
Use a fungicide labelled for cedar apple rust on susceptible apples, starting at pink bud stage and repeating through petal fall as the label directs.