Cedar-apple rust and related rusts: what the extension services record

This page describes what the named sources say. It is not a diagnosis of any tree and does not say what should be done with one. None of the four pages read lists these rusts as regulated or notifiable. Each section names its source, all read on October 9, 2026. The full list of diseases is on the tree diseases page.

Three rusts, two hosts each

The Morton Arboretum, the University of Wisconsin-Madison and Missouri Botanical Garden all name three closely related fungi in the genus Gymnosporangium: G. juniperi-virginianae (cedar-apple rust), G. globosum (cedar-hawthorn rust) and G. clavipes (cedar-quince rust). Each source says the fungus must infect two kinds of plant to finish its life cycle, a juniper and a woody member of the rose family. The Arboretum adds that eastern red cedar, Juniperus virginiana, is necessary to the fungus, that spores made on rose-family plants infect only junipers, and that spores made on the evergreen infect only rose-family plants. Clemson calls the fungus a native of North America and says that because it needs both hosts in the area, it is most common where forested and agricultural land mix.

Wisconsin points out that the names mislead, since all three diseases can affect several rose-family hosts besides the ones in their names.

Hosts by rust

Rust	Rose-family hosts named	Source
Cedar-apple rust	Primarily apples and crabapples; Clemson also lists hawthorn and flowering quince	Missouri Botanical Garden; The Morton Arboretum; Clemson
Cedar-hawthorn rust	Hawthorn, apples and crabapples; sometimes pears, quince and serviceberry	Missouri Botanical Garden; University of Wisconsin-Madison
Cedar-quince rust	The broadest range of the three: mountain-ash, flowering quince, cotoneaster, chokeberry, photinia and many other genera of the rose family; the Arboretum and Wisconsin note it on hawthorn, including stem cankers on Washington hawthorn	Missouri Botanical Garden; The Morton Arboretum; University of Wisconsin-Madison

Missouri Botanical Garden says all three rusts can infect most varieties of eastern red cedar and many other junipers. Wisconsin says Chinese junipers tend to be relatively resistant, and that pines, firs, spruces and flowering trees such as cherry, plum and lilac are immune.

On the juniper

The sources describe brown galls on juniper twigs that swell in spring rain and push out orange, jelly-like spore horns. Clemson calls them telial horns and says they appear in early spring after wet weather and can dehydrate in hot dry spells and revive after rain. Branch tips beyond a gall can die back, and heavily infested trees can look decorated. The size figures differ by source.

Source	Gall size recorded
Clemson	Swell up to 2 inches across
University of Wisconsin-Madison	Cedar-apple rust about 1/4 to 2 inches; cedar-hawthorn rust about 1/8 to 9/16 inch; cedar-quince rust makes branch swellings that ooze orange spores instead of galls
Missouri Botanical Garden	Cedar-apple rust galls often over 2 inches; cedar-hawthorn galls rarely over 2 inches
The Morton Arboretum	Pea-sized to an inch or more, brown to dull red and globular, with circular pits where the horns form

On timing, Missouri Botanical Garden says galls appear about seven months after infection and form spore masses after 18 months. The Arboretum says the fungus spends a full year on the juniper, and that galls on the juniper do not become evident until July of the following year. The Arboretum says dried galls stay attached for several years, with some small twig and tip dieback. Missouri Botanical Garden says usually no significant damage occurs on the juniper.

On apple, crabapple and hawthorn

Missouri Botanical Garden and the Arboretum both place yellow or yellow-orange circular spots on the upper leaf surface shortly after bloom or in late spring. Missouri Botanical Garden says wet, rainy weather in early spring favours infection, and heavy rain in the first two weeks of bud break and leaf expansion makes the disease worse. The Arboretum says about a month after crabapples have bloomed the spores are exhausted and most leaves are no longer susceptible, and that the first yellow spots show ten to 14 days after infection. Later, tube-like structures with a fringed look form under the spots. Wisconsin dates leaf symptoms of cedar-apple and cedar-hawthorn rust to mid to late May, and says cedar-quince rust becomes obvious later in summer, mostly on hawthorn, as swollen, spiny branches or fruit.

The Arboretum also lists a swollen corky gall on new twigs, usually no more than an inch long, and larger spots on fruit, with poor fruit quality or early drop. Clemson says infected apple and crabapple fruit are disfigured. In late summer the rust spots release spores that travel to nearby junipers, which restarts the cycle.

How far the spores travel

The Arboretum says spores can disperse up to 5 miles from a juniper, though most infections develop within several hundred feet. Clemson says they can drift up to several miles. Missouri Botanical Garden says spores can travel long distances on the wind, which is why it calls the value of removing galls or junipers debatable.

Outcome and status

Wisconsin calls these rusts primarily cosmetic, rarely with long-term harm. Clemson says repeated infections can severely weaken trees and that heavy leaf drop can hit apples, while the disease generally does not kill them. Missouri Botanical Garden says it rarely kills trees. None of the four pages names a quarantine, a notifiable status or a report line. This page gives no product names, rates or timings. For another rose-family disease on the same host list, see fire blight.