Cedar-hawthorn rust is a common disease of apple, crabapple, hawthorn, and ornamental pear in Kentucky; it also affects quince, mountain ash, pear, and serviceberry. The pathogen overwinters as galls on its alternate hosts, cedar and juniper. Removal of these galls on cedar can later reduce disease incidence on the deciduous hosts. Once trees become infected limited management options are available.
Cedar-Hawthorn Rust Facts
- Leaf symptoms begin as small, pale yellow spots on upper leaf surfaces (Figure 1). Spots enlarge to become orange with black dots in the center. Infected fruit, petioles, and twigs exhibit similar symptoms.
- In mid-summer, small orange-yellow tubular fruiting bodies project from lower sides of leaf spots or from fruit (Figure 2). Severely infected leaves and fruit may drop prematurely.
- The pathogen requires more than one host to complete its life cycle. Cedar and juniper serve as alternate hosts. In mid-late summer, spores from deciduous hosts are blown to evergreen alternate hosts. Infection results in the formation of galls (swellings), which expand over a period of 2 years before producing spores that infect deciduous hosts.
- Primary infection begins in early spring during leaf expansion.
- Damp conditions with temperatures between 50° to 60°F favors disease development.
- Caused by the fungus Gymnosporangium globosum.
- Select cultivars that are resistant or immune to cedar-hawthorn rust.
- Maintain plant health with proper nutrition and irrigation practices.
- Destroy nearby unmanaged, abandoned, or wild hosts.
- Prune and destroy galls found on juniper and cedar.
- Fungicides may be used preventatively during leaf expansion and flowering. Homeowners may use fungicides that contain myclobutanil or mancozeb. Always follow label directions when utilizing fungicides.
- Apple Rust Diseases (PPFS-FR-T-05)
- Backyard Apple Disease & Pest Management Using Cultural Practices (with Low Spray, No Spray & Organic Options) (PPFS-FR-T-21)
- Cedar-Hawthorn Rust, University of Illinois Extension (Link)
- Commercial Midwest Fruit Pest Management Guide (ID-232)
- Disease and Insect Control Programs for Homegrown Fruit in Kentucky including Organic Alternatives (ID-21)
- Fruit, Orchard, and Vineyard Sanitation (PPFS-GEN-05)
- Simplified Backyard Apple Spray Guides (PPFS-FR-T-18)
By Kim Leonberger, Plant Pathology Extension Associate and Nicole Gauthier, Plant Pathology Extension Specialist