Disease

Cedar-apple and related rusts

Gymnosporangium spp.

Rust fungi that need two hosts: juniper or red cedar, and apple, crabapple, hawthorn, pear or serviceberry. Spores from orange jelly horns on juniper galls in spring infect the apple-family leaves, and spores from those go back to the junipers from midsummer to early fall.

Signs

• Bright orange-yellow spots on apple-family leaves and fruit, later with tiny tubes or cups underneath.
• Brown, woody galls on juniper twigs that push out orange jelly-like horns in wet spring weather.
• Early leaf drop on susceptible crabapple and apple varieties.

What favors it

Juniper or red cedar within a few hundred feet of apple-family trees (spores can travel miles), and wet, mild spring weather when the jelly horns release spores.

Prevention

• Plant rust-resistant apple, crabapple and hawthorn varieties.
• Keep junipers and apple-family trees apart where you can.
• Prune galls off nearby junipers before the jelly horns form in spring.

Crops it shows up on

Apple, pear & stone fruit; Shade & ornamental trees; Evergreens & conifers (pine, spruce, juniper).

Often confused with

Sources

• Cedar-Apple RustMontana State University Extension
• Cedar-Hawthorn RustMontana State University Extension
• Cedar-Apple RustUW-Madison Plant Disease Diagnostics Clinic
• Cedar-apple rustUniversity of Illinois Extension

Why →