Cedar rusts: orange galls on the cedar, spots on hawthorn, crabapple and serviceberry
Why a cedar's brown galls sprout slimy orange tendrils in spring, how three related rusts differ, how far apart to plant the hosts, and what spraying cannot do.
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How the rust passes between cedar and crabappleTelling the three rusts apartHow much harm they doThe hosts we growDistance, pruning and the spray questionPlanting near a cedar or a crabappleCommon questionsSourcesThe brown galls on an eastern red cedar that swell into orange, jelly-like horns after spring rain are a cedar rust, a fungus with two hosts. Its spores blow from the horns onto crabapples, hawthorns and serviceberries. Their leaves then show yellow to orange spots. In late summer, spores from those spots blow back to the cedars. For most plants the rust is cosmetic, and fungicides are rarely recommended. Quince rust, which swells twigs and fruit more than it spots leaves, does more lasting harm.
How the rust passes between cedar and crabapple
These rusts live part of their lives on a juniper and part on a plant of the rose family, and spores from each host infect only the other. A cedar-apple rust gall takes 20 to 22 months to ripen. Through its second winter it is a hard brown ball up to 2 inches across, pitted like a golf ball.
In spring, around the time crabapples bloom, rain swells the galls into orange horns. Their spores ride the wind, mostly at night and in the early morning, and infect new leaves that stay wet for 4 to 6 hours. Yellow spots show 10 days to a few weeks later.
By midsummer, short tubes grow from the undersides of the spots. From mid-July to mid-September in southern New England, their spores blow back to the cedars and start the next galls.
Telling the three rusts apart
Three rusts share these hosts. Their names mislead, since each infects more plants than the one it is named for:
| Rust | On the cedar | On the leaves and fruit | Most often on |
|---|---|---|---|
| Cedar-apple rust | Round brown galls up to 2 inches, with horns 1/2 to 3/4 inch long | Yellow spots turning orange-red, with tiny tubes beneath | Apples and crabapples |
| Cedar-hawthorn rust | Smaller galls, 1/8 to about 1/2 inch, with shorter, fatter horns | Yellow to orange spots, with white tubes beneath | Hawthorns, apples and crabapples |
| Quince rust | No gall: swollen branches that ooze orange each spring for years | Swollen fruit and twigs bristling with white tubes, few leaf spots | Serviceberries, hawthorns and quince |
A fourth, juniper broom rust, grows dense clumps of twigs called witches’ brooms on the cedar and small spots on serviceberry leaves. Other leaf spots are sorted out in spots, powder and speckles on tree leaves.
How much harm they do
On the cedar, the galls do little harm, though the twig beyond one sometimes dies. A cedar-apple or cedar-hawthorn gall dies after its spring of spores, and it may hang on for a year or more. Pruning them off is for looks.
On the crabapples, hawthorns and serviceberries, spots do not significantly hurt a tree’s health unless the leaves fall. For most plants the damage ends there:
“Gymnosporangium rusts are primarily cosmetic diseases that make susceptible plants unattractive, but rarely have long-term detrimental effects. Gymnosporangium rusts on leaves can, for all practical purposes, be ignored.” (University of Wisconsin-Madison Extension, Gymnosporangium Rusts)
A very susceptible crabapple is the exception: heavy infection drops its leaves early, most of all in a dry summer, and years of it weaken the tree. A badly infected hawthorn’s leaves turn yellow and fall early too.
Quince rust attacks stems and fruit more than leaves. It swells and distorts hawthorn twigs, and on a shrub serviceberry its stem cankers start on shaded lower branches and spread upward, a dieback that worsens each year. Prune out an infected stem 4 to 6 inches below the swelling. Leaves that turn yellow without the orange spots point to other causes, the subject of yellow leaves in summer.
The hosts we grow
How hard the rusts hit differs by species. These are the hosts we grow with the clearest record:
| Plant | How the rusts treat it |
|---|---|
| American crabapple | Very susceptible to cedar-apple rust |
| Prairie crabapple | Very susceptible to cedar-apple rust, and leaf diseases can strip it before fall |
| Southern crabapple | Very susceptible to cedar-apple rust |
| Cockspur hawthorn | Rated resistant to cedar-hawthorn rust, yet that rust and quince rust are its main diseases near cedars |
| Downy hawthorn | Leaves prone to cedar-hawthorn rust, often dropping early by late summer |
| Green hawthorn | Among the most disease-resistant hawthorns, with some cedar-hawthorn rust near cedars |
| Mayhaw | Quince rust is its most common disease, severe on some wild trees in south Georgia |
| Washington hawthorn | Resists cedar-hawthorn rust, yet very susceptible to quince rust |
| Western mayhaw | Quince rust is its most common disease, severe in East Texas in 1990 |
| Downy serviceberry | Rust spots on leaves and fruit near cedars in humid springs |
| Saskatoon | Juniper rust among its usual diseases |
| Shadblow serviceberry | Rust can mark the leaves, though the damage is mostly cosmetic |
The rusts take the other hawthorns and serviceberries too, along with chokeberries and mountain ash. Apples and quince, which we do not grow, are hosts as well. Eastern red cedar is the usual juniper host, and creeping juniper and common juniper carry the rusts too.
Resistance to one rust says little about the next, in species and named selections alike:
“Rust-resistant cultivars of hawthorn are difficult to find. Often, a cultivated variety will have resistance to one of the rusts […], but be highly susceptible to, and very likely to be infected by a different rust […].” (University of Minnesota Extension, Cedar-apple rust and related rust diseases)
Distance, pruning and the spray question
Most infections come from cedars within a few hundred yards, but spores travel for miles and can infect hawthorns 15 miles away. Keeping the hosts that far apart lowers the rust without ending it, and in a small yard it may be impossible. The companions tool leaves the crabapples, hawthorns, serviceberries, chokeberries and mountain ash we grow out of eastern red cedar’s answer. It leaves the cedar out of theirs.
In late winter or early spring, before the horns form, cut the brown galls from small cedars nearby, 4 to 6 inches below each gall. Pruning lowers the spores reaching nearby hosts, though the Missouri Botanical Garden calls its worth debatable, since spores travel so far.
Do not spray the cedar: the rusts rarely do it noticeable harm, and a fungicide there will likely not work. On a crabapple or hawthorn, a fungicide only protects leaves not yet infected, so spraying once spots show does nothing. Protection would have to last from bud break until about a month after bloom, which is why spraying is rarely recommended. No fungicide has proved very effective against quince rust. These trees draw bees and other wildlife, one more reason to avoid fungicides where possible.
Planting near a cedar or a crabapple
Where cedars stand within a few hundred yards, plant a flowering tree the rusts cannot use. Plums and cherries are immune:
- American plum: fragrant white flowers an inch across in April and May, before the leaves. Zones 3 to 8, 15 to 25 feet.
- Chokecherry: spikes of fragrant white flowers 3 to 6 inches long, from April into June. Zones 2 to 10, 20 to 30 feet.
For an evergreen screen near crabapples or hawthorns, choose a pine, fir or spruce over red cedar. Native hedges, screens and windbreaks gives the trees and their spacing. Blue Whale Trees grows the plum and the chokecherry from seed, and both are among the small flowering trees in our shop.
Common questions
What are the orange slimy things on my cedar tree?
They are the spore horns of a cedar rust, most often cedar-apple rust, swelling from brown galls after spring rain. They shrivel when dry, and the gall dies after its one spring of spores.
Will cedar-apple rust kill my crabapple?
Rarely, since leaf spots alone do not harm a tree’s health unless the leaves fall. Years of early leaf drop can weaken a very susceptible crabapple, and quince rust can kill twigs.
How far should cedar trees be from apple trees?
A few hundred yards, since most infections come from cedars that close. Spores can travel more than a mile, so distance lowers the rust without ending it.
Should I spray my cedar tree for rust?
No: the galls do little harm to a cedar, and fungicides are not recommended there. On a crabapple or hawthorn, only a spray made before the spots appear does any good.
Sources
(8 references)
- Cedar-apple rust and related rust diseases: University of Minnesota Extension (Rebecca Koetter and Michelle Grabowski, reviewed 2026): the four rusts and their two families of hosts, gall and horn sizes, the symptoms on each host, juniper broom rust, galls dying after one spring, quince rust’s lasting cankers, the few hundred yards and the mile, gall pruning, the resistance quotation, and fungicides not recommended, useless after spots and hard on bees.
- Cedar-Apple Rust: UMass Extension Landscape, Nursery and Urban Forestry Program (Nicholas J. Brazee, 2024): spores at night and early morning, leaves wet 4 to 6 hours, the tubes and their spores from mid-July to mid-September, galls ripening in 20 to 22 months, infection mostly within a few hundred yards, and fungicides not recommended for the long infection periods.
- Cedar-Hawthorn Rust: UMass Extension Landscape, Nursery and Urban Forestry Program (Dan Gillman): galls of 1/8 to 1/2 inch, spots with tubes beneath by midsummer, hawthorns infected 15 miles away, cockspur and Washington hawthorn rated resistant, and no fungicide on the juniper.
- Cedar-Quince Rust: UMass Extension Landscape, Nursery and Urban Forestry Program (Nicholas J. Brazee, 2025): quince, hawthorn and serviceberry as its usual hosts, stem cankers and distortion, the worsening dieback of shrub serviceberries from shaded lower branches, and no fungicide found very effective.
- Cedar-Apple Rust: The Morton Arboretum: spore horns at crabapple bloom, spots 10 to 14 days after infection, leaf drop worst in dry summers, repeated infections weakening a tree, spraying after symptoms of no effect, the spores spent a month after bloom, and Washington hawthorn very susceptible to quince rust.
- Gymnosporangium Rusts (Cedar-Apple Rusts): University of Wisconsin-Madison Extension (Brian Hudelson, UW Plant Disease Diagnostics Clinic): the misleading names, quince rust’s branch swellings, the cosmetic quotation, pruning 4 to 6 inches below a gall, small yards, plums and cherries immune, and fungicides unlikely to work on junipers.
- Cedar-Apple Rust: Iowa State University Extension and Outreach, Yard and Garden: galls up to golf-ball size, little damage to cedars, and galls pruned from small cedars in late winter or early spring.
- Cedar-apple rust: Missouri Botanical Garden: pitted galls, spores that infect only the other host, the twig beyond a gall dying, dead galls hanging on a year or more, a disease that rarely kills, and the debatable worth of pruning galls.
