Cedar-Apple Rust vs Apple Scab: How to Tell the Difference
Learn to distinguish cedar-apple rust from apple scab, two common fungal diseases that affect apple and crabapple trees but have very different symptoms and management strategies.
At a Glance
Cedar-Apple Rust
MODERATE- Type
- Fungus
- Severity
- MODERATE
- Affected States
- 34 total (34 active)
Symptoms
Bright orange gelatinous spore horns on cedar galls in spring, yellow-orange spots on apple leaves and fruit, premature leaf and fruit drop on apples, round brown galls on cedar branches
Apple Scab
MODERATE- Type
- Fungus
- Severity
- MODERATE
- Affected States
- 26 total (26 active)
Symptoms
Olive-green to brown velvety spots on leaves, dark scabby lesions on fruit surface, leaf yellowing and premature drop, cracked and deformed fruit in severe infections
Similarities
What makes Cedar-Apple Rust and Apple Scab easy to confuse:
- Both are fungal diseases that commonly affect apple and crabapple trees
- Both can cause premature leaf drop and reduced fruit quality
- Both are favored by wet spring weather conditions
- Both can be managed with fungicide applications timed to spring infection periods
- Both benefit from selection of resistant cultivars for long-term management
Key Differences
| Feature | Cedar-Apple Rust | Apple Scab |
|---|---|---|
| Pathogen | *Gymnosporangium juniperi-virginianae* | *Venturia inaequalis* |
| Alternate host | Requires both cedar/juniper AND apple/crabapple to complete lifecycle | Only infects apple family; no alternate host needed |
| Leaf symptoms | Bright orange-yellow spots on upper leaf surface with tube-like structures beneath | Olive-green to dark brown velvety spots on leaves |
| Fruit symptoms | Orange spots similar to leaf lesions, minor deformation | Dark, scabby lesions on fruit surface; fruit may crack and deform |
| Unique feature | Produces gelatinous orange telial horns on cedar galls in spring rain | Causes "velvet" lesion texture; severe infections cause leaf curling |
| Cedar connection | Visible brown galls (1-2 inches) on juniper/cedar branches | No relationship to cedars or junipers |
How to Tell Them Apart
- Look at lesion color: Cedar-apple rust produces bright orange to yellow spots that are very distinctive and conspicuous. Apple scab produces olive-green to brown lesions that have a more muted appearance.
- Check the underside of leaves: Cedar-apple rust lesions develop tube-like structures (aecia) on the leaf underside that release orange spores. Apple scab lesions are similar on both leaf surfaces.
- Look for nearby cedars or junipers: If there are Eastern red cedars (junipers) within a few hundred yards with brown, golf-ball-sized galls on their branches, cedar-apple rust is likely. Apple scab does not involve cedars.
- Examine fruit lesions: Apple scab causes dark, rough, corky lesions on fruit. Cedar-apple rust causes bright orange spots on fruit without the rough scabby texture.
- Check the time of peak symptoms: Both are spring diseases, but cedar-apple rust spots appear slightly later than initial apple scab infections. Apple scab is usually the first foliar disease visible in spring.
Frequently Asked Questions
Can my apple tree have both diseases at once?
Yes, this is very common. Apple and crabapple trees frequently suffer from both cedar-apple rust and apple scab in the same season, especially in areas with abundant Eastern red cedars nearby. Both diseases may be present on the same leaf.
Should I remove cedar trees near my apple trees?
Removing Eastern red cedars within a few hundred yards can reduce cedar-apple rust pressure significantly. However, spores can travel up to a mile or more on wind, so complete elimination of the alternate host is often impractical. Resistant apple varieties and fungicide programs are usually more effective.
Which disease is worse for fruit production?
Apple scab is generally more damaging to fruit quality and marketability. Severe scab infections cause cracked, deformed fruit that is unsaleable. Cedar-apple rust usually causes cosmetic damage to fruit without major deformation.
What are the best resistant apple varieties?
Many modern apple cultivars have been bred for resistance to both diseases. 'Liberty,' 'Enterprise,' 'Freedom,' and 'GoldRush' are among the most disease-resistant varieties available. Check with your local extension service for varieties suited to your region.
When should I apply fungicides?
For both diseases, fungicide timing is critical. Applications should begin at green tip (when buds first show green tissue) and continue through petal fall. Most programs use applications at 7-10 day intervals during this period. Captan, myclobutanil, and mancozeb are common choices.