Cedar trees do not poison apple trees, and their roots do not compete in any special way. The trouble is a fungus. Eastern red cedar (Juniperus virginiana) and other junipers are one of two hosts for cedar-apple rust, and apples and crabapples are the other. The fungus needs both to finish its life cycle, so a cedar near an apple tree keeps the disease going year after year.
The short answer: yes, cedars can be bad for apple trees, because eastern red cedar and other junipers host cedar-apple rust (Gymnosporangium juniperi-virginianae). Spores from galls on the cedar blow to apple leaves in spring and cause bright yellow-orange spots, early leaf drop and poor fruit. The Morton Arboretum says spores can travel up to 5 miles, but most infections happen within several hundred feet. Planting rust-resistant apples is the most practical fix for home gardens.
How the disease moves between cedar and apple
The Morton Arboretum describes a two-year cycle. The fungus spends a full year on the juniper. During the second spring, usually around the time crabapples bloom, brown galls on the cedar soak up rain and swell. They push out orange, jelly-like spore horns. As the horns dry, wind carries the spores to young apple, crabapple and hawthorn leaves.
On the apple, small yellow spots appear 10 to 14 days after infection, according to Morton. Several weeks later, the underside of each spot develops orange or brown growths with hair-like tubes. In late summer these release a different type of spore that can only infect junipers, and the cycle starts again.
Clemson Extension adds two useful details. The spore horns can dry out and rehydrate after wet weather, producing new spores up to seven times in one season. Wind-carried spores can drift for several miles before landing on a host.
What cedar-apple rust does to an apple tree
On leaves
Bright yellow to orange spots form on the upper surface of the leaves in late spring. Clemson says the spots can reach up to half an inch across and merge into larger rusty patches. The undersides later show small bulges with tiny tubes. Heavily infected leaves may drop early, and Morton notes the defoliation tends to be worse in dry summers.
On fruit
Fruit gets yellow to orange spots that are usually larger than the leaf spots. Morton says fruit infection lowers quality or causes the apples to drop early. Clemson notes that badly infected apples and crabapples can be disfigured and inedible.
On twigs
Young twigs can develop small, swollen, corky galls, usually no more than an inch long. Badly affected twigs are stunted and may die.
Is it fatal?
Usually not. Clemson says the disease generally does not kill trees, but repeated years of infection weaken them and make them less able to resist other pests and diseases. If you are trying to work out whether a tree is dying for other reasons, see our guide to what kills juniper trees for the cedar side of the picture.
What it looks like on the cedar
The juniper shows a very different stage. Galls start as brown or dull red growths that range from pea-sized to an inch or more across, according to Morton. Clemson describes them swelling up to 2 inches and covered in small ring-shaped dimples. After spring rain, they sprout bright orange gelatinous horns, which makes infected trees look almost decorated. Twigs beyond a gall can die back, and old galls stay on the tree for years.
The cedar itself is not badly harmed in most cases. The damage that matters to a gardener is on the apple side.
How far apart should cedars and apples be?
There is no distance that guarantees safety, because spores travel on the wind:
| Distance | What the sources say |
|---|---|
| Several hundred feet | Where most infections develop (Morton) |
| 1 mile | Separating the hosts by this distance “will help reduce infection” (Morton) |
| 2 to 3 miles | Radius of cedar removal some commercial orchards use (Clemson) |
| Up to 5 miles | Maximum spore travel distance (Morton) |
For a home garden, removing every cedar within a mile is rarely possible, and the cedars may belong to neighbors. Clemson calls cedar removal over a 2 to 3 mile radius impractical for most homeowners. Removing one cedar right next to your apple may still lower the number of spores landing on it, because most infections come from nearby, but it will not end the problem if more junipers grow in the area.
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How to protect apple trees
Plant resistant apples
This is the most reliable option. Morton recommends planting resistant trees and notes that many apples, crabapples, hawthorns and junipers show resistance. The University of Maryland Extension marks cultivars with some resistance to cedar-apple rust in its home garden apple list. Check the description before you buy, because some popular scab-resistant varieties are still susceptible. For example, UMD lists ‘Florina’ as resistant to fire blight, powdery mildew and scab, but somewhat susceptible to cedar-apple rust.
Remove galls from cedars you own
Morton advises removing galls and cankers from junipers to reduce infection of the alternate host. Clemson suggests pruning galls in late winter to early spring, before they produce spore horns.
Prune infected apple growth
Clemson says pruning infected leaves and branches on apple and crabapple can slow the spread within the tree.
Protective sprays
Fungicides only work before infection. Morton says spraying after symptoms appear has no controlling effect. Its timing for apples and crabapples is to begin when new growth appears and flower buds show color but are not yet open, then repeat three to four times at labeled intervals. Clemson notes that some fungicide options it describes are for ornamental trees only, not trees grown for fruit. Always read the label to confirm a product is approved for edible apples, and avoid spraying open blossoms that pollinators visit.
Cedar-apple rust versus other apple leaf problems
Cedar-apple rust spots are bright and orange in spring and early summer. Late-summer yellowing with dark brown or black spots points to other causes, such as the fungal disease apple blotch. Our guide on why apple leaves turn yellow walks through how to tell them apart. Pears get a related rust from junipers too; see our guide to treating rust on pear trees.
The bottom line
Cedars and apples can share a yard, but expect cedar-apple rust on susceptible apples in most years. Choose a resistant apple, keep galls off any junipers you own, and if you spray, start before the leaves are infected. Clemson lists cedar-apple rust among the common apple diseases, so in a region full of red cedars, a resistant apple saves the most work.
Sources
- Cedar-Apple Rust, The Morton Arboretum
- Cedar-Apple Rust (HGIC), Clemson Cooperative Extension
- Growing Apple and Pear Trees in a Home Garden, University of Maryland Extension
- Apple (HGIC 1350), Clemson Cooperative Extension
Top photo: Littleinfo, Public domain, via Wikimedia Commons