Cedar-Apple Rust
Gymnosporangium juniperi-virginianae
Overview
A heteroecious rust disease requiring two hosts to complete its life cycle: junipers (cedars) and apples/crabapples. Produces distinctive orange, gelatinous galls on junipers and yellow-orange spots on apple leaves.
Symptoms
On apples: bright yellow-orange spots on upper leaf surfaces with tube-like projections (aecia) on undersides. Fruit may develop similar lesions. On junipers: brown, golf-ball-sized galls that produce orange, gelatinous tendrils in spring rain.
Environmental Conditions
Humid
Prevention
Plant rust-resistant apple varieties. Remove nearby junipers if possible (within 1-2 miles). Remove galls from junipers before spring. Apply preventive fungicides on apples from pink bud through petal fall.
Management
Apply myclobutanil or sulfur fungicides on apples during spring infection period. Remove galls from junipers in winter. Remove heavily infected leaves. Maintain tree vigor.