Cedar-Apple Rust is a fungal rust disease caused by Gymnosporangium juniperi-virginianae. The disease depends on two hosts, the Eastern Red Cedar (Juniperus virginiana) and apple or crab apple trees. The disease causes relatively minor, but economically important, infections in apples in the summer. The rust spores are blown onto Eastern Red Cedars where they produce galls in which the fungus over-winters before beginning the cycle again.
The galls are quite beautiful.
When it rains in the Spring, the fungus develops orange, gelatinous telial horns.
After the rain, the horns dry up and release spores that then infect apple trees.
As the gall ages, it may form artistic sculptures
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- Cornell University Plant Disease Diagnostic Clinic: Cedar-Apple Rust (Gymnosporangium juniperi-virginianae)
- Plant of the Week: Apple-Cedar Rust