Cedar-Apple Rust
Risk near you, next 48h
See whether your local forecast favours this disease right now.
When it strikes
Treat, then re-check in 5–7 days
Pick off the worst material, apply the organic option below, and look again after five to seven days. If the spread continued, escalate rather than repeating the same treatment.
Rain and irrigation splash
Water splashing off soil and infected leaves carries it upward and along the row. Watering at the base and mulching the soil surface break the route.
It carries over to next season in soil, debris or seed — which is why rotation matters here, not just treatment.
Hot compost only
A heap that reaches and holds 55–65°C throughout will destroy it. A cool corner heap will not, and will return the problem to the beds with the finished compost.
When and where to look
Scout the planting while temperatures hold between 8°C and 24°C, with humidity above 85%, after rain or heavy dew, while the leaves are still wet. Risk builds after roughly 6 unbroken hours of those conditions, so the morning after such a night is the moment to look.
Rule these out first
Same category, and at least one host crop in common — so they are genuinely confusable in the same part of the garden.
The signs that lead here
Full problem lists for these crops
About
Cedar-apple rust (Gymnosporangium) needs both junipers and apples to complete its life cycle, spotting apple foliage and fruit after wet spring weather when orange spores release from cedar galls.
Symptoms
Bright yellow-orange spots on apple leaves and fruit that develop tube-like structures beneath; on junipers, brown galls produce gelatinous orange horns when wet.
Organic Treatment
Remove nearby juniper galls before spring rains, rake apple leaf litter, and apply sulfur during the infection window.
Chemical Treatment
Myclobutanil applied from pink bud through early fruit development.
Prevention
Separate apples from junipers, plant resistant apple cultivars, and prune galls from cedars in late winter.
Crops at risk
Related problems
Cedar-Apple Rust risk by location
Each location has a month-by-month profile computed from the weather archive: how many hours a year actually meet this disease’s thresholds.