Cedar-Apple Rust: Life Cycle, Apple Impact, and Fungicide Control

Understanding the Disease Cycle

Cedar-apple rust requires two hosts: juniper/cedar and apple/crabapple. The gelatinous orange galls on cedars in spring release spores that infect apples. Cedar galls (golf-ball sized) cause minimal cedar damage but are the infection source for apples.

Apple Symptoms and Damage

• Bright yellow-orange leaf spots (1/8-1/4 inch) in late spring
• Spots enlarge, turn orange with black fruiting centers
• Orange gelatinous matrix oozes during wet weather
• Cup-like structures on leaf undersides produce dusty spores
• Premature defoliation weakens trees, reduces fruit set
• Fruit lesions: deep pits, distortion, premature drop

Fungicide Treatment Schedule

First spray: When gelatinous tendrils appear on cedar galls
Continue: 7-10 day intervals while galls active (usually through May)

Effective Fungicides

• Myclobutanil (Immunox, Eagle, Systhane, Rally) — controls both rust and scab
• Triforine (Funginex) — apples only
• Chlorothalonil (Daconil 2787) — crabapple only
• Triadimefon (Bayleton)
• Ferbam

Note: Captan and benomyl (for scab) don't control rust. Check labels for host-specific registration (apple vs. crabapple).

Cedar Management

Galls can be pruned by April 1. Rust rarely kills cedars; limb breakage likely unrelated. If no apples nearby, cedar treatment unnecessary—spores travel up to 2 miles.