Quick facts
- Cedar-apple rust and related rust fungi need plants from two plant families to complete their life cycle; Cupressaceae family (eastern red cedar and other junipers) and Rosaceae (apple, hawthorn, serviceberry).
- Bright orange to red leaf spots occur on apples, hawthorns, and other plants in the Rosaceae family.
- Hardy woody galls, witches brooms and swollen stems covered in gummy, orange, fungal growth in spring occur on juniper and eastern red cedar.
- These fungi rarely cause serious damage to their hosts and do not require management in most cases.
- This disease can cause damage to leaves and fruit of very susceptible apple varieties, but is only a minor problem on resistant or partially resistant trees.
- Do not plant eastern red cedar and juniper within a few hundred yards of apples, hawthorns, and other plants from the Rosaceae family.
- Disease resistant varieties are available for some plants.
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These diseases require plants from two different families in order to complete their life cycle; one plant from the Cupressaceae family (red cedar, juniper) and the other from the Rosaceae family (crabapple, hawthorn, serviceberry). Symptoms are very different on each type of plant.
Cedar-apple rust
- Disease is most common on apple and crabapple. It occurs occasionally on hawthorn.
- Leaf spots are first yellow then turn bright orange-red, often with a bright red border.
- Small, raised, black dots form in the center of leaf spots on the upper leaf surface when the leaf spots mature.
- Very short (less than 1/10th inch), finger-like fungal tubes stick out from the lower surface of the leaf, directly below leaf spots.
- The fungal tubes appear fringed when they open at the tip to release yellow to orange, powdery spores.
- Rarely, green to brown irregular spots with black dots form on the fruit surface. Fruit spots do not extend deep into the fruit.
Hawthorn rust
- Disease is most common on hawthorn, apple and crabapple. It occurs occasionally on serviceberry, quince and pear.
- Leaf spots are yellow to orange. Raised, black dots form in the center of the spots on the upper leaf surface as they mature.
- White, finger-like, fungal tubes (up to 1/8th inch long) stick out from the underside of leaf spots.
- When infection is severe on hawthorn, leaves turn completely yellow and fall prematurely.
- Infection of green stems occurs occasionally and can result in thick, deformed growth of stems. This can cause shoot death when severe.
- Rarely found are orange to rust colored, spore-filled blisters on the fruit surface.
Quince rust
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- Disease occurs in over 480 species of Rosaceae family including serviceberry, chokeberry, hawthorn, apple, crabapple, cotoneaster, pear and mountain ash.
- White, finger-like fungal tubes develop all over fruit and stick out up to 1/8 inch.
- Tubes rip open at the tip to release powdery, bright orange spores.
- Leaves are often unaffected. A few yellow spots may be found on leaves.
- Infected areas of stems bulge to become elongated and distorted.
Juniper broom rust
- Disease affects serviceberry, apple and crabapple, hawthorn and mountain ash.
- Leaf spots are small, yellow, slightly raised and may have a red border.
- Raised, gummy, yellow droplets form in the center of leaf spots and eventually turn into raised, black dots.
- In highly susceptible hosts, leaf tissue around the leaf spot dies. The spot then turns brown (with a red border) and expands from the infection point to the leaf edges in a wedge shape.
- Infected leaf veins cause the leaf to curl and become distorted.
- Small, yellow spots with red borders are found on green stems, leaf petioles (leafstalks) and leaf veins.
- Finger-like tubes develop on leaf petioles (leafstalks), stems and occasionally develop on upper and lower sides of leaf veins.
Cedar-apple rust
- Disease is most common on Eastern red cedar (Juniperus virginiana) and Rocky Mountain juniper (J. scopulorum).
Disease occurs occasionally on Chinese juniper (J. chinensis), creeping juniper and low juniper (J. communis var. depressa). - In fall, round, woody galls can be found on twigs and small branches. These galls are greenish-brown and up to 2 inches in diameter.
- In wet spring weather, these galls produce orange, gummy, tentacle-like projections that are 1/2 to 3/4 inch long.
- When dry, the gummy orange structures shrivel to a dry, reddish-brown. Galls can dry and rehydrate several times in one spring.
Hawthorn rust
- Disease is most common on Eastern red cedar (J. virginiana) and Rocky Mountain juniper (J. scopulorum).
- Disease occurs occasionally on Chinese Juniper (J. chinesis), creeping juniper (J. horizontalis), low juniper (J. communis var. depressa) and Savin juniper (J. sabina).
- Small, reddish-brown, woody galls form along needles and stems. These galls can be round or irregularly shaped and from 1/10th inch to just over 1/2 inch in size (smaller than cedar-apple rust galls).
- In spring, bright orange, gummy horns form. These horns have straight, blunt fingers that are shorter and fatter than cedar-apple rust galls.
Quince rust
- Disease occurs on Eastern red cedar (J. virginiana), common juniper (J. communis), creeping juniper (J. horizontalis), Rocky Mountain juniper (J. scopulorum), and Savin juniper (J. sabina).
- Branches and twigs swell from infection.
- Later, these infected areas become elongated and their bark begins to peel.
- In spring, small, orange, gummy blobs come out of swollen areas and cracks along infected branches.
Juniper broom rust
- Disease occurs on creeping juniper (J. horizontalis), Eastern red cedar (J. virginiana), and Rocky Mountain juniper (J. scopulorum).
- Round clumps of foliage can be seen anywhere in the tree canopy.
- These clumps are clusters of many small branches called witches’ brooms.
Swollen, elongated areas with rough, cracked bark can be seen on infected branches without witches' brooms. - Orange jelly forms on needles and from cracks in infected bark during wet spring weather.
- Brooms usually die when small but a few survive and may reach 20 to 24 inches in diameter.
Japanese apple rust is caused by Gymnosporangium yamadae, a fungus native to Asia. While this disease has been found in the Eastern U.S., it has not been identified in Minnesota. Like other Gymnosporangium rusts, this exotic disease spends part of its life on apples or crabapples and the other part on Chinese (J. chinensis) and flaky juniper (J. squamata).
- Produces round, woody galls on the branches of Juniper (similar to cedar-apple rust).
- In spring, these galls produce orange, gummy projections.
- These projections stick out like rubbery shelves but do not dangle like the horns on Cedar-apple rust galls.
- On apple trees, leaf spots are bright red with a pale cream to white center.
- Infection on apple fruit is rare.
- Long, finger-like, fungal spore producing structures come out of the underside of leaf spots in mid to late summer.
- These structures produce and release chestnut-brown, powdery spores.
Suspected cases of Japanese apple rust should be reported to the Minnesota Department of Agriculture's 'Arrest the Pest' at 1-888-545-6684 or arrest.the.pest@state.mn.us.
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How do cedar apple rust and related rust fungi survive and spread?
Although cedar-apple rust is the most well known, there are actually four different rust fungi that cause similar diseases on the same types of trees in Minnesota. All four require plants from two different families to complete their life cycle; one plant from the Cupressaceae family (red cedar, juniper) and the other from the Rosaceae family (crabapple, hawthorn, serviceberry, etc.). These four related rust diseases have very similar life cycles and biology.
- Cedar-apple rust and related rust fungi over-winter in infected branches and galls on juniper and red cedar trees.
- In wet, spring weather, the galls produce orange, gummy, fungal growth that release spores.
- During dry spring weather, the orange, gummy structures shrivel and dry.
- Galls can rehydrate and dehydrate several times in one season in response to weather conditions.
- Once weather becomes consistently warm and dry, spores are no longer produced on infected junipers or red cedar trees.
- After one season of spore release, galls of cedar-apple rust and hawthorn rust die and fall off the tree.
- Cankers of quince rust and witches' brooms of juniper broom rust go dormant but may survive for multiple years, releasing new spores each spring.
- Spores produced on infected junipers and red cedar trees are carried by wind to susceptible apple, hawthorn or other plants in the Rosaceae family.
- These spores can infect trees over a mile away.
- If leaves and fruit are wet, spores are able to start new infections.
- Leaf spot and fruit infections grow slowly over the summer.
- Powdery yellow, orange or chestnut-brown spores are released from infected leaves and fruit mid to late summer.
- These spores cannot infect trees in the Rosaceae family. They must be carried by wind to start new infections on young needles and shoots of juniper or red cedar trees.
- It takes up to two years for galls to form on the juniper or red cedar tree.
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How to manage cedar apple rust and related rust diseases
Cultural Control Practices
- Tolerate leaf spots and fruit infection on apples, hawthorns, serviceberry and other plants in the Rosaceae family. They do not significantly affect the health of the tree if leaf loss does not occur.
- Do not plant eastern red cedar and juniper plants within a few hundred yards of susceptible Rosaceae plants. This will reduce diseases problems but not completely eliminate them.
- Inspect nearby juniper and red cedar trees in late winter or early spring. Prune and remove brown, woody galls found before orange, gelatinous structures form in the spring. This will help reduce the level of infection on nearby Rosaceae plants.
- Prune and remove infected twigs or branches on Rosaceae plants if they occur.
Resistant varieties
Rust resistant cultivars of hawthorn are difficult to find. Often, a cultivated variety will have resistance to one of the rusts (such as cedar-apple rust) and be highly susceptible (very likely to be infected by) to a different rust (such as hawthorn rust).
Plant disease-resistant varieties of crabapple and apple when possible. Do not plant Beacon and Wealthy apple varieties in areas where cedar apple rust has been a problem in the past. Among apple varieties commonly grown in Minnesota, these are the only two that are likely to be significantly damaged by rust.
Cedar-apple rust resistant apple and crabapple varieties that are hardy in Minnesota
Apple
- Fireside
- Freedom
- Liberty
- Nova
- Easygro
- Novamac
- Redfree
Crabapple
- Adams
- Adirondack
- Beverly
- Candied Apple
- Dolgo
- Donald Wyman
- Eleyi
- Ellwangerina
- Henry Kohankie
- Indian Summer
- Liset
- Lollipop
- Mt. Arbor
- Narragansett
- Ormiston Roy
- Persicifolia
- Purple Prince
- Red Baron
- Red Jewel
- Robinson
- Robusta
- Royalty
- Sargent cv. Tina
- Snowdrift
- Special Radiant
- Zumi
Reference: Adapted from Diseases of Tree and Shrubs, Sinclair and Lyon, 2005.
Fungicides
- Fungicides are not recommended to protect trees from infection with cedar apple rust and related rust fungi. Trees and shrubs often tolerate infection.
- There are no fungicides available to home gardeners that can be used on trees where the fruit will be eaten by people.
- Fungicides are available to protect trees and shrubs that are for ornamental purposes only.
- Fungicides with the active ingredient Myclobutanil are most effective in preventing rust. Copper and sulfur products can be used as well.
- Fungicides are only effective if applied before leaf spots or fruit infection appear
- Spray trees and shrubs when flower buds first emerge until spring weather becomes consistently warm and dry.
- Monitor nearby junipers. Fungicides need to be applied to crabapple, hawthorn, serviceberry and other rosaceae plants when gelatinous orange spore producing structures appear on galls and branches.
Trees and shrubs in the Rosaceae family are highly attractive to bees, birds, and other wildlife. Avoid using fungicides if possible.
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- Galls and witches' brooms on eastern red cedar or junipers do little harm to the tree or shrub and do not need to be managed.
- Galls and witches' brooms can be pruned off to improve the look of the tree or shrub.
- Quince rust cankers should be pruned out of the tree or shrub. The pruning cut should be made several inches below visible signs of the canker to make sure the fungus is completely removed from the tree or shrub.
- Fungicides are not recommended to protect eastern red cedar or junipers from infection.
Resistant varieties
Some resistant varieties of juniper and eastern red cedar are available and should be used in areas where Gymnosporangium rusts are a known problem.
Chinese juniper (Juniperus chinensis)
- Ames
- Blue point*
- Foemina*
- Fortunei*
- Hetzii*
- Hetzii Columnaris
- Iowa
- Japonica*
- Keteleer
- Leeana*
- Maney
- Mas*
- Mountbatten
- Perfecta
- Plumosa*
- Aurea*
- Pyramidalis*
- Robusta Green
- Spartan
Common juniper (J. communis)
- Aurea*
- Aureospica*
- Cracovia*
- Depressa*
- Hibernica*
- Oblonga Pendula*
- Saxatilist*
- Suecica*
- Suecica Nana*
Creeping juniper (J. horizontalis)
- Admirabilis*
- Adpressa*
- Argenteus*
- Douglasii*
- Eximius*
- Filicina*
- Glomerata*
- Livida*
- Petraea*
- Plumosa*
Eastern red cedar (J. virginiana)
- Aurea*
- Berg's Rust Resistant*
- Blue Mountain
- Burkii*
- Globosa*
- Grey Owl
- Hillspire
- Kosteri*
- Pseudocupressus*
- Pyramidalis*
- Skyrocket*
- Tripartita*
- Venusta*
Flaky or Himalayan juniper (J. squamata)
- Alob-variegata*
- Meyeri*
- Wilsonii*
- Farges' weeping juniper*
Pfitzer juniper 'Sea green' (J. xpfitzerian)
- Pfitzer juniper 'Sea green'*
- Compacta*
- Glauca*
Rocky Mountain juniper (J. scopulorum)
- Medora
- Moonglow
Sargent juniper (J. chinensis var. sargentii)
- Variegata*
- Wateri*
- Wintergreen
Savin juniper (J. sabina)
- Savin juniper*
- Broadmoort*
- Fastigiata*
- Knap Hill*
- Tamarix juniper*
*Plants also resistant to hawthorn rust
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Reviewed in 2019
Cedar-apple rust is a disease which is caused by a fungus belonging to the genus Gymnosporangium. It commonly affects apple and crabapple trees. Gardenerdy lists out a few effective ways to get rid of cedar-apple rust.
It was a Danish botanist named Anders Sandøe Ørsted who explained the two-year (19-22 months) disease cycle of the cedar-apple rust. An unusual fungus, Gymnosporangium juniperi-virginianae is a heteroecious rust that requires two host plants to survive.
Cedar-apple rust is common in areas where Malus domestica (apple), Malus sylvestris (crabapple), and other species from the Malus genus grow near Eastern red cedar, ornamental junipers, or other plants belonging to the Juniperus genus. This fungus spends a part of its life cycle on junipers, and the rest on rosaceous hosts such as apple and crabapple. Closely related to this rust are cedar-hawthorn rust and cedar-quince rust, which are caused by Gymnosporangium globosum and Gymnosporangium clavipes, respectively. These are fungi that belong to the same genus, and also need two hosts to complete their life cycle.
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Being a fungus, Gymnosporangium juniperi-virginianae thrives in damp, moist environment. The signs of this fungal disease can be seen after the first rain in the spring. This rust overwinters in the form of ½-2 inch wide, kidney-shaped brown galls (outgrowths that are covered with small depressions) on the twigs of cedars or junipers. The fungus starts growing after the first rain in early to mid-spring. When the galls become wet, they produce gelatinous tendrils or telial horns that are made of two-celled teliospores. Each of these teliospores produces four basidiospores. The microscopic spores produced by these gelatinous telial horns are carried by the wind. The spores that land on apples or crabapples germinate, thereby infecting these trees. The following sections list out the symptoms of cedar-apple rust fungus, along with ways to get rid of cedar-apple rust.
Signs of Cedar-apple Rust on Apples/Crabapples
◆ Greenish-yellow spots on the leaves of apple and crabapple (Early June)
◆ Change in the color of the spots (orange to red, depending on the cultivar)
◆ Spots on the upper and lower surface of the leaves
◆ Formation of spore cups (aecia) on the lower surface of the leaves
Aeciospores that are released from the cups in mid-summer to autumn are carried by the wind. These infect only the junipers, and not the apple or crabapples.
Signs of Cedar-Apple Rust on Junipers
The disease cycle continues after junipers are infected. The signs of an infestation include:
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◆ Formation of galls on cedars or junipers
◆ Development of bright telial horns, which become gelatinous after rain
After the development of gelatinous telial horns, basidiospores are produced and carried by the wind. As many as 7.5 million basidiospores may be produced in a single gall. These spores land on the apple/crabapple trees, and germinate and infect the leaves.
How to Get Rid of Cedar-Apple Rust
Cedar-apple rust fungus causes galls on junipers, which can sometimes cause dieback of twigs. However, it doesn’t cause significant damage in junipers. In severe cases, cedar-apple rust can cause defoliation and fruit loss in apples/crabapples. Here are some ways to get rid of this fungus:
Eliminate One of the Host Plants
As this fungus requires two host plants to complete its life cycle, removing one of the hosts can help prevent damage. As a part of their life cycle, the spores produced by the telial horns are carried by the wind. If there’s an apple/crabapple tree in the vicinity, the spores could land on them, which in turn can lead to an infestation. So, if a few juniper trees are present around the apple/crabapple in the area, these could be removed. Eliminating one of the hosts can help in preventing an infestation.
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Basidiospores that are produced on a juniper are often short-lived. More often than not, infections occur due to spores that are produced by a juniper located within a few hundred feet from the apple or crabapple tree. So, if the two host plants are located about a mile apart, it is advisable to remove one of them. Separating the two host plants by a distance of 2-3 miles can minimize the possibility of this fungal infection.
Grow Varieties that are Resistant to Cedar-Apple Fungus
There are a few apple/crabapple cultivars that are resistant to the cedar-apple rust. These include:
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◆ Red Delicious
◆ McIntosh
◆ Arkansas Black
◆ Winesap
◆ Mollies Delicious
◆ Spartan
◆ Priscilla
◆ Liberty
◆ Empire
If you live in the Eastern part of the Rocky Mountain region, avoid growing apple cultivars that are known to be susceptible to this fungus. Here are the names of some of the varieties that are prone to getting infected by this fungus:
◆ Prima
◆ Sir Prize
◆ Lodi
◆ McLemore
◆ Jono
◆ Jonathan
◆ Rome
◆ Golden Delicious
◆ Jonafree
Pruning
Pruning the affected parts (galls) of the juniper tree can also lower the possibility of infections to some extent. It is advisable to prune the host plants during the dormant season, which is winter. The fungus begins to grow in the early spring, after the first rain. So, make sure that you remove the galls before the spring. Also, dispose off the dead or fallen leaves from under the trees. In severe cases, the entire plant or tree may have to be removed or destroyed.
Application of Fungicides
Besides the aforementioned methods, apple and crabapple trees can be protected from the spores produced by the junipers by applying fungicides. The spores are produced in spring, which is why organic fungicides can be applied weekly on apple and crabapple trees from the time the buds begin to form. The release of spores only occurs during the spring, which is why fungicides don’t need to be applied after spring. More often than not, the fungicide includes chlorothalonil, mancozeb, propiconazole, sulfur, myclobutanil, or copper soap.
Fungicides should be applied to the juniper trees at the time when aecia develop on apple or crabapple trees. It is advisable to use fungicides that are registered for use in your area. Also, if the apples/crabapples will be harvested for consumption, make sure that you use fungicides that are registered for use on edible fruits. Make sure that you read the label properly, and follow the instructions provided by the manufacturers regarding the application of the fungicide.
On a concluding note, refrain from planting apple/crabapple trees next to or around junipers. In case you notice the signs of an infestation, follow the aforementioned ways to get rid of cedar-apple rust.