Cedar Apple rust treatment

Apples With Cedar Apple Rust: How Does Cedar Apple Rust Affect Apples

Growing apples is usually pretty easy, but when a disease strikes it can quickly wipe out your crop and infect other trees. Cedar apple rust in apples is a fungal infection that affects both the fruit and the leaves and affects apples and crabapples alike. The infection is not uncommon but control is possible.

Cedar Apple Rust on Apple Trees

Cedar apple rust is a fungal infection caused by the species Gymnosporangium juniper-virginianae. It is often confused with other rust infections but is completely different. What makes cedar apple rust really unique is its life cycle. The fungus requires two completely different host plants to complete a cycle.

It infects apples and crabapples in the spring and then juniper plants in the late summer. The fungus is much more damaging to its apple hosts than its juniper hosts.

How Does Cedar Apple Rust Affect Apples?

The infection can be severe and can ruin your apple crop if not controlled. Even more moderate infections can be damaging. The damage to leaves will cause them to drop early, especially in dry conditions. After a few seasons, the trees become weak and the apple crop will drop off. The infection also reduces the production of fruit buds on a tree.

Managing Cedar Apple Rust in Apples

Apples with cedar apple rust need special care to overcome the disease and still produce fruit. First, check to see if you have juniper species near your apple trees. If they are infected, they will produce galls in the spring and summer that can grow quite large. They produce distinctive orange tendrils that are hard to miss. Spores from these can infect any nearby apple trees.

One way to manage the disease is to remove or destroy any nearby junipers. Or you can just monitor them for galls and either destroy the plant or prune off and destroy the branches with galls. Another way to control for cedar apple rust is to grow varieties of apple that are resistant to the infection: Red Delicious, McIntosh, Winesap, Empire, and others.

A fungicide spray can also be used. Your local nursery can help you find the appropriate spray. However, prevention is usually a better way to control this disease in apple trees. About 1,000 feet between apples and juniper species is enough to protect your trees. Also, keep in mind that a low level of infection will not affect your crop very much.

Q: I’m hoping you can help me. My husband usually takes care of the yard work, but he’s a firefighter and just left for Fort McMurray. He beautifully shaped and pruned our three juniper trees about a month ago, and this fungus-type flower recently blossomed. I know that he’s going to come home exhausted so I want to take care of this for him, if I can. What treatment do you recommend, and do we need to be worried about our other trees and bushes? I’ve attached a photo, and any suggestions you have would be sincerely appreciated.

A: First, thank you to your husband for his service. The brave men and women firefighters are truly appreciated. Our thoughts and prayers are with them and the people of Fort McMurray.

The problem you are describing is cedar-apple rust — a fungus. On evergreen hosts (like junipers) you will see the formation of balls that look like brown apples. When mature, they send out these bizarre-looking, gelatinous orange fingers. On deciduous hosts such as hawthorn and apple, the leaves will begin to show yellow spots. Over time these spots will turn orange and eventually develop into black spots. By mid-summer you can see tiny tubes forming on the undersurface of the leaves.

Once infected, there is no treatment for the current season. Pruning out the growth is the most effective way to reduce infection. Make sure to disinfect your pruners between cuts, using a solution of one litre of water and two tablespoons of bleach. No chemical treatment is completely effective, but application of a fungicide may help in reducing the problem.

I know that there used to be several fungicides on the market for treating the problem, but those have been removed from sale. As I did more research, I kept finding that many experts are recommending the use of sulphur as a means of treating cedar-hawthorn and cedar-apple rusts. Your local garden centre will carry a garden sulphur spray. Start spraying in the spring, when the buds begin to form and swell, and then again after the buds open, and once more about 10 days after they open. You can also try using a copper spray as both a preventative and control. Most major garden centres will also carry a commercially prepared copper spray.

Cedar-apple rust will affect some members of the rose family, such as hawthorns, apples and Saskatoons, but should not affect rose bushes.

Q: I have read your column faithfully for years. We grow lots of kale, but the last few years the aphids are terrible. After picking the leaves, we take the aphids off with hot/warm water before getting the leaves ready for the winter. What can we do to eliminate the problem?

A: Thank you for being a faithful reader. Washing off the aphids is a good idea, but I know you are looking for a somewhat easier method. There are chemicals that can be used to control the problem, although I hesitate to advise using them since this is a food crop. My best advice would be to use an insecticidal soap, but you will need to apply it faithfully for several applications because the aphids will keep on hatching. One application will not be enough. You may need as many as four or five applications.

It’s easy to make your own insecticidal soap solution using pure soap, not liquid dish detergent. Pure soap can be found in health food stores — castile soap is an example. Mix one tablespoon of soap to one gallon of water and spray the solution directly on the aphids. The solution will kill on contact, but must reach the aphids in order to work. Keep an eye out for further hatchings and wash the kale very well before consuming.

I cannot stress enough how important it is to watch out for hatchings and spray regularly. Most gardeners give up after the first two applications, and it is actually easy to control aphids if you have patience. For me, patience is a far better route to go than using chemicals.

Gerald Filipski is a member of the Garden Writers Association of America. E-mail your questions to [email protected] He is the author of Just Ask Jerry. To read previous columns, go to edmontonjournal.com/filipski

Cedar-apple rust

There are several cedar-rust diseases that spend part of their life cycle on Eastern red cedar (Juniperus virginiana) and other junipers, and another part of their life cycle on apple, hawthorn, and other members of the rose family. Both hosts are required for the fungus to complete its life cycle. The three most common rusts occurring in Illinois are caused by Gymnosporangium juniperi-virginianae (cedar-apple rust), G. globosum (cedar-hawthorn rust), and G. clavipes (cedar-quince rust).

DISEASE CYCLE

The rust organism spends one full year of its life cycle on junipers. During the second spring, usually around the time crabapples are in bloom, the galls become rain soaked and swell, producing jelly-like tendrils (spore horns) that project out of the galls. As the spore horns begin to dry, the spores are released and carried by the wind to young, newly developing leaves of hawthorns and other susceptible plants. Dispersal of spores can range up to 5 miles from a juniper but most infections develop within several hundred feet. About a month after crabapples have bloomed, the spores are exhausted and most leaves are no longer susceptible. Ten-to-14-days from initial infection, small yellow spots can be seen on upper surfaces of infected leaves. Several weeks later, the fungus appears as orange or brown spots with hairlike appendages on the underside of the leaf. In late summer, the rust spots release the spores and are carried to nearby junipers.

Cedar-apple rust is the most common of the three fungal rust diseases and attacks susceptible cultivars of apples and crabapples. It infects the leaves, fruit, and, occasionally, young twigs. The alternate host plant, Eastern red cedar (Juniperus virginiana), is necessary for the survival of the fungus. Spores produced on rose family plants only infect juniper plants, and those originating on the evergreen host only infect rose family plants. Repeated infections of cedar-apple rust can be unsightly and seriously weaken and destroy the ornamental value and health of susceptible plants.

Symptoms on Apple and Crabapple

On leaves: Bright yellow/orange spots develop on the upper surface of the leaves in late spring. These spots gradually enlarge, becoming evident on the undersurface of the leaves as small bulges. In midsummer, these rust lesions develop hairlike, cylindrical tubes (hyphae), which release spores into the air that are blown to the juniper host. Infected leaves of apples and crabapples may drop, with defoliation more severe in dry summers. Galls that form on the juniper host do not become evident until July the next year, requiring two years for the fungus to complete its life cycle.

On twigs: The rust appears as a swollen corky gall on the current year’s growth, usually no more than 1 inch in length. The swelling eventually develops the characteristic cylindrical fruiting bodies. Seriously affected twigs are stunted and may die.

On fruit: The rust causes yellow to orange spots similar to those found on the leaves, but the spots are usually much larger. Fruit infection causes an inferior fruit quality or premature fruit drop.

In mid-spring, swellings or galls develop on juniper needles that were infected with spores during the previous year. These galls are brown to dull red in color, globular in shape, and may vary from pea-sized to an inch or more in diameter. As they mature, circular pits or depressions are found over the surface of the galls. After spring rains and damp weather, yellow gelatinous tendrils or spore horns form in these pitted areas. The tendrils elongate rapidly and release spores during dry, windy weather that follows the spring rains. Spores produced on the juniper host are then blown to the apple, crabapple, and hawthorn hosts as their new growth emerges.
Eventually the galls dry out but remain attached to the tree for several years, resulting in some small twig and tip dieback.

CEDAR-HAWTHORN RUST

Cedar-hawthorn rust is very similar to cedarapple rust, both in appearance and occurrence, but infects a broader range of plants within the rose family. The severity of the disease is usually minor on crabapples and apples (Malus sp.), mountain ash (Sorbus), and pears (Pyrus), but can be quite serious on many hawthorns (Crataegus sp.).

Symptoms on Hawthorn

On leaves: Large yellow spots appear on cedar-hawthorn rust the upper surface of the leaves turning yellow orange to gray-brown as the spores mature. When rust is severe, all the foliage may turn bright yellow and drop prematurely. The orange leaf spots are smaller on apple and crabapple.

On fruits and twigs: Deformation of fruits and young twigs is particularly severe on hawthorns, but this damage is usually caused by the cedar-quince rust fungi and not cedar hawthorn rust fungi.

On juniper: Cedar-hawthorn rust galls are smaller in size than cedar-apple rust galls, less symmetrical, and more chocolate-brown in color. Galls remain on the twigs of branches of junipers for several years, where they continue to produce spores, compared to the one season spore production of cedar-apple rust.

CEDAR-QUINCE RUST

Cedar-quince rust affects quince (Chenomeles), serviceberry (Amelanchier), hawthorn (Crataegus), mountain ash (Sorbus) and many other plants in the rose family. Though generally not as prevalent as cedar-apple rust, it causes the greatest amount of damage to the fruits, twigs, and thorns of susceptible plants. During extended periods of wet weather, when temperatures range between 50 degrees F and 75 degrees F, severe infection can occur just four hours after initial leaf contact.

Symptoms of leaves: Basically none, occasionally veins or petioles will be swollen.

On twigs and thorns: Elongated swollen cankers appear on twigs and thorns. In damp weather, orange to brown spores are visible.

On Junipers: Spindle-shaped swelling occurs on twigs and branches of junipers. Young branches are usually girdled, then die. In damp weather, older galls are covered with masses of gelatinous, orange to brown spore horns. Galls can produce spore horns for 4 to 6 years, sometimes longer.

DISEASE MANAGEMENT

Cultural Control
Because this disease requires two hosts, the separation of the hosts for a distance of one mile will help reduce infection. Ideally, to minimize disease host availability, plant trees and shrubs that are resistant to rust diseases. There are many apples, crabapples, hawthorns, and junipers that exhibit resistance to these diseases. The Morton Arboretum publication Crabapples for the Home Landscape provides information on selecting crabapples.

Chemical Control
Protective fungicides can be applied to help minimize infection. A minimum of three applications should be done. These applications protect the new leaves from spores that are dispersed from the juniper host in mid-spring. Spraying apple, crabapple, and hawthorn foliage after symptoms develop has no controlling effect.
Apples and Crabapples: Begin spraying when new growth appears and flower buds show color but are not yet open. Repeat three to four times at 10 to 14 day intervals.

Hawthorns:
Spray as new growth appears and flower buds begin to open. Repeat 3 to 4 times at labeled intervals. Washington hawthorns are very susceptible to quince rust and form noticeable stem cankers that should be pruned out.

Junipers:
Begin spraying susceptible plants in early July and continue at labeled intervals through August. Remove galls and cankers to reduce infection of alternate hosts.

Contact the Plant Clinic (630-719-2424 or [email protected]) for current recommendations.

Gymnosporangium juniperi-virginianae

Rusts are fungi that will not kill their hosts, although they sure make them suffer. There is even a term for pathogens that require living hosts: biotrophs (in contrast to necrotrophs, pathogens that kill their host and live off the dead tissue).

Think Gloria Gaynor – your plants will survive! However, repeated infections of this pathogen can seriously weaken and destroy the health of susceptible plants. They will also lose any ornamental value.

Read on to learn how to identify and control cedar apple rust in your garden or home orchard.

What Is Cedar Apple Rust?

Cedar apple rust (Gymnosporangium juniperi-virginianae) is a fungal disease that depends on two species to spread and develop.

It spends a portion of its two-year life cycle on Eastern red cedar (Juniperus virginiana).

The pathogen’s spores develop in late fall on the juniper as a reddish brown gall on young branches of the trees.

The galls growing in this juniper represent a threat to your fruit production.

As the spring showers begin, the galls grow and release spores, which are carried by the wind to infect apple and crabapple trees. There, they develop into a disease that causes red spots to occur on the leaves, and that can deform the fruit.

The damage done to the leaves greatly affects the apple trees’ ability to gather sunlight and nutrients from the air, damaging its health and fruit production, and in some cases causing death.

This fungal pathogen can damage leaves to the extent that infected trees will die if left untreated. Photo by Mike Quinn.

The fungus cannot be transferred from apple tree to apple tree, or from juniper to juniper.

The following year, spores are released from the apple trees that, in turn, infect the junipers.

The disease is extremely prolific during wet years.

Note that this is a simplified explanation. Gymnosporangium juniperi-virginianae actually produces FIVE different kinds of spores.

When a Cedar Is not a Cedar

All native American cedars, including Western and Eastern varieties, are not true cedars. They are actually a form of juniper. True cedars are native to hot and arid Mediterranean locations such as Lebanon and Cyprus, and the Himalayas.

Both are are conifers and belong to the taxonomic Pinales order. But the American natives belong to the the cypress family (Cupressaceae) while the true varieties are of the pine family (Pinaceae).

True cedars have fan-like foliage and produce small cones or pink flowers, while junipers have rough textured bark similar to that of many hardwoods, and they usually have scale-like leaves and reddish stringy bark.

Symptoms on Juniper

This fungal pathogen starts life on junipers as an aeciospore that the wind carries from apples to its new host in the late spring or early fall. A brown gall develops the following summer and fall.

Not only do the galls on junipers look like an organism from a bad 1960s sci-fi movie, the fungus’s reproduction process is something usually found only in a Star Trek episode.

During the spring rains 18 months later comes a metamorphosis that rivals that of Kafka’s. Instead of turning into a cockroach, the galls swell and grow spurs called telial horns that are brown at first, but turn bright orange in the rain.

Apple cedar rust is straight out of the disco era with its large galls and radically orange telial horns that protrude in all directions. To make them even more outrageous, the telia are gelatinous.

If conditions are right, these telial horns produce another type of spore that produces yet another kind of spore, which is blown back to infect apple leaves and fruit. As few as 4-5 hours of rain at 50-75°F is time enough to produce a severe infection on apples.

Symptoms on Apples and Crabapples

Instead of galls, infected apple and crabapple trees manifest circular yellow spots on the upper surface of their leaves soon after bloom. Later in the summer, brownish cylindrical tubes with hairs sticking out appear underneath the yellow spots, or on the twigs and fruit.

Signs of Gymnosporangium juniperi-virginianae on apple tree leaves. Photo by Mike Quinn.

These tubes produce the aeciospores that will complete the cycle by infecting the needles of junipers.

At the least, the infected fruit may be of marginal quality. Worst case scenario – they drop off the tree.

In addition, a severe infection can cause your tree to drop its leaves! If that happens for several years in a row, your apple tree could be in peril.

How to Control Cedar Apple Rust

The best way to control cedar apple rust is to prevent infection using a mixture of cultural methods and chemical treatments.

If you see the lesions on the apple leaves or fruit, it is too late to control the fungus. In that case, you should focus on purging infected leaves and fruit from around your tree.

Spraying apple trees with copper can be done to treat cedar apple rust and prevent other fungal infections. Photo by Mike Quinn.

Don’t plant junipers near rust-susceptible plants, which include both apples and crabapples. Consider resistant apple varieties, such as ‘Freedom,’ ‘Liberty,’ ‘Redfree,’ or ‘William’s Pride.’

And also destroy wild or unwanted apples, crabapples, or junipers, so they won’t infect your apple tree.

Cultural Controls

Since the juniper galls are the source of the spores that infect the apple trees, cutting them is a sound strategy if there aren’t too many of them.

While the spores can travel for miles, most of the ones that could infect your tree are within a few hundred feet.

The best way to do this is to prune the branches about 4-6 inches below the galls.

You will want to disinfect your pruning shears, so you don’t spread the infection. Dip them in 10% bleach or alcohol for at least 30 seconds between cuts.

Fungicide Treatments

If your tree has a history of infection with cedar apple rust, you will want to get ahead of the infection and take preemptive measures.

This is critical in the spring, when the juniper galls are releasing their spores.

The time to treat your tree is between the pink stage of the blossoms (when the leaves are turning green) to the period when the petals drop.

The most effective types of fungicides to use are those that inhibit fungal sterols. They are known as “SI,” or sterol inhibitors.

In the old days, sprays for apple scab would also take care of cedar apple rust. However, this is no longer the case.

The fungus that causes apple scab is now frequently resistant to the sterol-inhibiting fungicides, and manufacturers have moved on to using newer classes of fungicides. Only certain types of fungicides are effective.

Extension agents at North Carolina State University attribute this trend to an increase in occurrences on apple trees in the state.

Unfortunately, captan, the fungicide in many pre-mixed sprays for home fruit trees, does not work on on this particular fungal pathogen.

Several extension agencies recommend that you use Immunox® to control cedar apple rust. It contains myclobutanil as its active ingredient.

Spectracide Immunox Multi-Purpose Fungicide Spray Concentrate via Amazon

Make sure you choose a formulation that is labeled for use on fruit trees such as the one shown above, since several types available today are not designed for this purpose.

Typically, you should spray every 7-10 days during the period of infection. After that, you no longer need to treat your tree for the rest of the year.

Organic Controls

You have several options if you want to avoid using traditional fungicides on your apple tree.

Biofungicides

There is a strain of bacteria that is effective at treating cedar apple rust on apple trees. It is a special strain of Bacillus subtilis, sold commercially as Serenade® Garden Disease Control.

Serenade® Garden Disease Control (Bacillus subtilis) via ARBICO Organics

One plus of this treatment is that it is nontoxic to beneficial insects and honeybees.

A Mixture of Sulfur and Pyrethins

These two classic compounds are available in a pre-mixed spray known as Bonide® Orchard Spray.

This spray controls both fungi and insects and is certified organic. Beware that it can harm beneficial insects in the area along with pests.

BONIDE® Citrus, Fruit & Nut Orchard Spray via ARBICO Organics

Be sure to spray all parts of your tree – especially the new leaves.

Liquid Copper

You can treat them with a solution of copper at least four times. Use 0.5 to 2.0 ounces of copper per gallon of water.

BONIDE® Liquid Copper Fungicide in a three-gallon backpack sprayer. Photo by Mike Quinn.

It’s best to start with this treatment as a preventative early in the spring before the trees are showing signs of infection, or just as they begin showing symptoms.

BONIDE® Liquid Copper Fungicide

Copper is not a cure-all, but it can help greatly in preventing damage to the leaves and fruit.

You can find this product in most farm and home stores (such as Tractor Supply) or you can purchase it through ARBICO Organics.

Should You Treat Junipers?

Although the galls don’t do much damage to junipers, treating them with fungicide can help prevent their spores from spreading. This can also help to reduce the amount of cedar apple rust on your tree.

The time to treat the junipers is before the galls produce their teliohorns, or when they are producing the aeciospores.

You can treat them with a liquid copper product like you would with apple trees.

Unfortunately, you need to treat them repeatedly from mid-summer until fall, which can be expensive.

Other Fungal Rusts

Additional rusts plague apples and crabapples in addition to other types of fruit. These other fungal diseases have life cycles similar to that of cedar apple rust, but their telial phases are less dramatic.

Cedar-hawthorn rust (Gymnosporangium globosum) affects pear, serviceberry, and quince.

Additional alternate hosts include Rocky Mountain juniper, common juniper, and prostrate juniper. Its telial phase is short and stubby, and its spots on apple or crabapple leaves are initially yellow and then turn orange.

Cedar-quince rust (G. clavipes) affects many plants in the rose family.

Additional alternate hosts include common juniper, prostrate juniper, Rocky Mountain juniper, and savin juniper. In this case, the galls are much less noticeable – basically swellings on the juniper twigs. The telial phase looks like oozing orange scum.

And unlike the other rusts, the cedar-quince fungus typically infects thorns, new twigs, and fruits on its fruit host. These infections are much less dramatic, too, with spots that are barely noticeable.

Try as They Might, These Fungi Cannot Hide

One of the few good things about these fungi, except that they rarely kill your plants outright, is that they are really hard to miss. You will know when you see those orange telial horns on junipers that you should work on protecting your apple or crabapple tree right away.

With these tips from Gardener’s Path, you have hope of tamping down the cedar apple rust on your apple or crabapple trees.

Leave a comment if you have dealt with this nasty fungus, and let us know how it turned out for you. Have any more tips to suggest? Sharing is caring!

Read on for more tips about apple diseases:

  • How to Prevent and Control Powdery Mildew on Apple Trees
  • How to Identify and Control Sooty Blotch and Flyspeck on Apples
  • How to Identify and Control Apple Black Rot and Frogeye Leaf Spot

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Photos by Mike Quinn © Ask the Experts, LLC. ALL RIGHTS RESERVED. See our TOS for more details. Product images via Spectrum Group, Bayer, and Bonide. Uncredited photos: . With additional writing and editing by Mike Quinn and Allison Sidhu.

About Helga George, PhD

One of Helga George’s greatest childhood joys was reading about rare and greenhouse plants that would not grow in Delaware. Now that she lives near Santa Barbara, California, she is delighted that many of these grow right outside! Fascinated by the knowledge that plants make chemicals to defend themselves, Helga embarked on further academic study and obtained two degrees, studying plant diseases as a plant pathology major. She holds a BS in agriculture from Cornell University, and an MS from the University of Massachusetts Amherst. Helga then returned to Cornell to obtain a PhD, studying one of the model systems of plant defense. She transitioned to full-time writing in 2009.

Gymnosporangium Rusts

Authors: Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 01/23/2019
X-number: XHT1009

Cedar-apple rusts form slimy, orange fruiting body on junipers in early spring.

What are Gymnosporangium rusts? Gymnosporangium rusts are a group of closely related diseases caused by fungi that infect both junipers (in particular red cedar) and woody plants in the rose family (such as, but not limited to, apple, crabapple, hawthorn and quince). These fungi must infect both types of plants to complete their life cycles. The most common Gymnosporangium rusts found in Wisconsin are cedar-apple rust, cedar-hawthorn rust and cedar-quince rust. The names of these diseases are somewhat misleading, given that all three diseases can affect multiple rosaceous hosts in addition to those referenced in their names.

What do Gymnosporangium rusts look like? On junipers, symptoms of Gymnosporagium rusts vary. Cedar-hawthorn and cedar-apple rust fungi induce formation of irregularly-shaped brown galls, with cedar-hawthorn rust galls tending to be smaller in size (approximately 1/8 to 9/16 inch in diameter) than cedar-apple rust galls (approximately 1/4 to 2 inches in diameter). Both types of galls produce distinctive slimy, orange, gelatinous appendages in the spring. In contrast, the cedar-quince rust fungus causes juniper branch swellings. Orange spores ooze from these swollen areas in the spring.

On rosaceous hosts, Gymnosporangium rust symptoms also vary. Symptoms of cedar-hawthorn rust and cedar-apple rust appear in mid to late May, typically as circular, yellow-orange areas on leaves. Eventually, tube-like structures (that have a fringe-like appearance) form on the undersides of leaves beneath the yellow spots. Symptoms of cedar-quince rust typically become obvious later in the summer (most commonly on hawthorns) as swollen, spiny branches and/or fruits.

Circular, yellow-orange diseased areas typical of cedar-apple rust on apple.

Where do Gymnosporangium rusts come from? Several fungi in the genus Gymnosporangium cause Gymnosporangium rusts. These include Gymnosporangium juniperi-virginianae (cedar-apple rust), Gymnosporangium globosum (cedar-hawthorn rust), and Gymnosporangium clavipes (cedar-quince rust). These fungi overwinter in infected branches and galls on junipers. Spores oozed from the infected branches or produced in the gelatinous gall appendages drift to rosaceous hosts leading to leaf and fruit infections. Similarly, spores produced in the tube-like structures/spines on rosaceous leaves and fruits drift to junipers leading to new branch infections and additional gall formation.

How do I save a tree or shrub with Gymnosporangium rust? 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. Gymnosporangium rusts on juniper branches can be easily managed by pruning approximately four to six inches below swollen areas or galls. Rosaceous hosts with infected branches can be pruned similarly. Be sure to decontaminate pruning tools between cuts by dipping them for at least 30 seconds in 70% alcohol (e.g., rubbing alcohol) or 10% bleach. Alternatively, you can spray tools with a disinfectant that contains approximately 70% alcohol, then allow them to air dry. Decontaminating tools will prevent movement of rust fungi from branch to branch or from plant to plant during pruning.

How do I avoid problems with Gymnosporangium rusts in the future? The best way to avoid Gymnosporangium rusts is to not grow junipers (particularly red cedar) and susceptible rosaceous hosts close to one another. In urban settings where yards are small however, keeping both hosts adequately separated may be impossible. Where Gymnosporangium rusts have consistently been a problem, consider using evergreens (e.g., pine, fir, spruce) and flowering trees and shrubs (e.g., cherry, plum, lilac) that are immune to these diseases. If you decide that you want to mix junipers with apple, crabapple, hawthorn, and quince on your property, check at your local nursery for resistant varieties that will satisfy your landscaping needs. In general, Chinese junipers (Juniperus chinensis) tend to be relatively resistant to Gymnosporangium rusts.

Cedar-quince rust on hawthorn fruit.

Fungicides treatments are also available to control Gymnosporangium rusts, although such treatments should be considered only as a last resort. Among fungicides marketed for use by home gardeners, those containing chlorothalonil, copper, mancozeb, myclobutanil, propiconazole, and sulfur are labeled for use for Gymnosporangium rust control. These products may be useful for controlling Gymnosporangium rusts on rosaceous hosts, but will likely not be particularly effective if used on junipers. For optimal control on rosaceous hosts, apply treatments when flower buds first show color, when half of the flowers are open, at petal-fall, seven to 10 days after petal fall and finally 10 to 14 days later. Be sure to read and follow all label instructions of the fungicide(s) that you select to ensure that you use the products(s) in the safest and most effective manner possible. In particular, be sure that you select appropriate products when treating trees and shrubs with edible fruit. If you decide to use propiconazole or myclobutanil, alternate use of these active ingredients with use of at least one of the other active ingredients listed above (but DO NOT alternate propiconazole with myclobutanil) to help minimize potential problems with fungicide-resistant strains of Gymnosporangium.

Tags: apple, disease, rust Categories: Fruit Problems, Tree & Shrub Problems

Tips For Cedar Apple Rust Control

If you’re noticing unusual-looking, green-brown growths on your cedar tree or having a bad apple crop, you may have been infected by cedar apple rust disease. While this fungal disease causes more damage to apples than it does cedar, it’s still important to learn how to prevent its occurrence.

What is Cedar Apple Rust?

Cedar apple rust, or CAR, is a peculiar fungal disease that affects both apple trees and red cedar. Spores from one tree only affect the other and vice versa. For instance, the spores on apple trees only infect cedar while the spores found on cedar trees only affect apples. This disease can quickly defoliate apple trees and cause blemishes on the fruit.

Signs of Cedar Apple Rust Disease

CAR fungus overwinters in large, brown galls (called cedar apples). Following the warm, spring rains and during the pink apple blossoming stage, these galls begin to form gelatin-like tendrils (telia) that within months produce fungal spores that are released in summer. These spores travel, land, and germinate on apple trees in a continuous back and forth cycle.

While adequate moisture is necessary before apples become infected, rust lesions may begin to appear on the leaves and fruit within one to two weeks following infection. With apple, it first appears on the foliage as small greenish-yellow spots that gradually enlarge, becoming orange-yellow to rust colored with a band of red. The undersides of the leaves begin forming the spore-producing lesions, which are cup-like in nature. They may also appear on the young fruit, leading to malformation of the fruit.

On cedar, the upper and inner foliage becomes infected in summer with small greenish-brown galls. These continue to grow in size, turning a dark brown by autumn and then overwintering in the tree until spring.

Cedar Apple Rust Control

While there are cedar apple rust fungicides available for its control, the best method of control is to prevent cedar apple rust from spreading. Galls may be removed from trees before reaching the telia stage by pruning them from the cedar trees in late winter.

Removal of any nearby red cedar (usually within a two-mile radius) and the use of resistant apple varieties can also help. Of course, removing all the cedars may not be practical for everyone, so using cedar apple rust fungicides would then be your best recourse. These fungicides should be applied periodically during the pink stage of apple bud development and continued throughout the season to protect emerging leaves and developing fruit.

Most recommended schedules and fungicides are available through local extension services.

Cedar-apple rust is a fungus disease of apple and cedar and spends parts of its life cycle on each host. It is caused by Gymnosporangium juniperi-virginianae. The fungus can infect leaves and fruit of most cultivars in the eastern region. This table lists the susceptibility of various apple cultivars to cedar apple rust.

Apple cultivar Cedar-apple rust susceptibility rating (z) Apple cultivar Cedar-apple rust susceptibility rating (z)
Ambrosia HS Mollies Delicious VR
Arkansas Black R Monroe S
Arlet HS Mutsu S
Baldwin VR Niagra R
Barry R Northern Spy S
Beacon S Northwestern Greening S
Ben Davis S Orin S
Braeburn HS Paulared R
Britemac R Prima HS
Burgundy S Pink Lady S
Cameo HS Pinova HS
Carroll R Princess HS
Chinook HS Priscilla R
Crimson Crisp HS Puritan R
Creston HS Quinte S
Dayton R Raritan S
Delblush VR Redfree VR
Delicious VR Rhode Island Greening S
Early McIntosh R Rome Beauty HS
Empire R Runkel VR
Enterprise VR Sansa VR
Fortune R Scarlet O’Hara HS
Fuji HS Scotia R
Gala HS Senshu S
Gala Supreme VR September Wonder S
Ginger Gold HS Shizuka HS
Gloster S Spartan R
Golden Delicious HS Spigold HS
Golden Supreme R Spijon S
GoldRush HS Stark Bounty S
Granny Smith R Stark Splendor S
Gravenstein Holly VR Starkspur earliblaze R
Grimes Golden R Stayman S
Hampshire VR Summerred HS
Honeycrisp S Suncrisp R
Idared S Sundance VR
Jamba S Sunrise S
Jerseymac VR Twenty Ounce HS
Jonafree S Viking R
Jonagold S Wayne S
Jonamac R Wealthy HS
Jonathan HS Williams Pride S
Julyred S Winesap R
Liberty VR Winter Banana HS
Lodi HS Wellington R
Macoun R Yakata S
Maiden Blush R Yellow Transparent R
McIntosh VR York Imperial HS
Milton VR Zestar! VR
(z)

VR = very resistant. No control needed. (Very few cultivars in this category for any disease.)

R = resistant. Control needed only under high disease pressure.

S = susceptible. Control usually needed where disease is prevalent.

HS = highly susceptible. Control always needed where disease is prevalent. These cultivars should receive first priority when control is required.

See Cedar-Apple Rust and Table of Juniper, Hawthorn, and Crab Apple Resistant to Rust Diseases for more information.

Disease-Resistant Apple Cultivars


Division of Plant Sciences

Disease infection is a major limitation to growing apples in Missouri. Several cultivars with apple scab immunity or resistance are currently available for planting. Although these cultivars can reduce pesticide usage, apples are susceptible to other diseases and insect pests. All the cultivars listed below are immune or resistant to apple scab. Because temperatures often reach 100 degrees F in August, early-ripening disease-resistant cultivars are excluded. Also, some cultivars have not yet been evaluated in Missouri and may have unidentified limitations to fruit production.

Figure 1. Planting apple cultivars that are resistant to prevalent diseases may eliminate the need to apply fungicides. (Sketch by Barbara Barkwell Long)

Apple cultivars

  • Liberty
    An older cultivar, released in 1978, that has broad resistance to apple scab, fire blight, cedar apple rust and powdery mildew and, therefore, is highly recommended for planting in Missouri. It has red fruit with a yellow background color that generally ripens around Sept. 10 in central Missouri.
  • Pixie Crunch
    Pixie Crunch is immune to apple scab, moderately susceptible to fire blight and susceptible to downy mildew and cedar-apple rust. Trees have a spreading growth habit with some bare wood on their leggy branches. This red apple ripens about the same time as Liberty and the fruit tends to be small, but it has a crisp texture.
  • Crimson Gold
    Trees of this cultivar have a moderate growth habit and are resistant to apple scab but may be susceptible to other diseases. Apples are yellow with a reddish-orange blush, have a sweet/acidic flavor and ripen around early September.
  • Crimson Topaz
    Trees have an upright, vigorous growth habit and are resistant to apple scab but only moderately resistant to mildew and fire blight. Fruits are medium-size and yellow with reddish-orange striping. Harvest in mid-September.
  • Freedom
    A scab-resistant cultivar released by the New York State Agricultural Experiment Station breeding program. Trees are only moderately resistant to fire blight. The fruit has a spicy flavor and an orangish-red peel. In wet growing seasons, it may be susceptible to black rot.
  • Galarina
    This cultivar has high tolerance to scab, but its susceptibility to other diseases has not been evaluated in Missouri. Apples have a sweet flavor, with medium-size to small reddish orange fruit. Fruit resembles that of Gala and is harvested in mid- to late September.
  • Florina (Querina)
    Another scab-resistant cultivar, originating from France. It also has moderate resistance to blight and mildew but is susceptible to cedar apple rust. Its parentage includes Jonathan. The dark red, medium-size fruit has a sweet/tart flavor and ripens in October.
  • Enterprise
    An older, but reliable cultivar that ripens in October. It is immune to scab, resistant to fire blight and cedar apple rust, and moderately resistant to mildew. The fruit is tart and is medium to large with red color, and the peel tends to be tough.
  • Goldrush
    This cultivar is immune to apple scab and moderatly resistant to powdery mildew and fire blight but susceptible to cedar apple rust. It has medium to large yellow fruit with sweet/acidic flavor that tends to mellow when cold-stored. The fruit ripens in October after Enterprise.

Common disease symptoms

  • Apple scab
    Apple scab is caused by a fungus that infects the fruit and the foliage of trees under cool, humid conditions in spring. Young, velvety brown lesions can be seen on the underside of leaves. With time, individual lesions may coalesce and infect the upper and lower leaf surfaces. A severe infection of the leaves can cause premature defoliation, which reduces tree growth and yield. Scab lesions on the fruit are brown and corky. As the fruit enlarges, it may grow unevenly, resulting in misshapen, cracked fruit. Fruit losses from apple scab can be severe on susceptible cultivars.
  • Cedar apple rust
    Because plantings of eastern red cedar (Juniperus virginiana) are widespread in Missouri, cedar apple rust is another common disease in the state. Eastern red cedar serves as an alternate host to the disease. Under rainy conditions in spring, galls on the cedar branches produce orange, gelatinous horns that release spores. Wind can carry the spores as far as a mile to infect the young leaves and blossoms of apple trees. After infection, orange-brown lesions appear on the upper sides of the foliage or on fruit. On susceptible cultivars, cedar apple rust can cause defoliation and loss of fruit quality. Goldrush, Pixie Crunch, and Florina are susceptible to cedar apple rust and should be avoided in areas where cedar apple rust is prevalent.
  • Fire blight
    Fire blight is a devastating bacterial disease that occurs in most parts of Missouri. This disease infects blossoms, fruit, branches and leaves. Infected tissue appears black, as if scorched by fire. The “shepherd’s crook” symptom, in which the shoot tips are bent over, is the most easily recognized evidence of the disease. Whole branches or trees may be lost after fire blight infection. Fire blight infection favors temperatures higher than 65 degrees F and moisture. Enterprise and Liberty cultivars are very resistant to fire blight, but others are susceptible to the disease.
  • Powdery mildew
    Powdery mildew is caused by a fungus that infects blossoms, fruit and leaves. Whitish, felt-like patches can be seen on the underside of foliage. Infected floral buds open five to eight days later than healthy ones. Later, the developing fruit often exhibits russetting, which appears as brown, corky netting on the surface of the small apples. Powdery mildew infection favors cool temperatures and high humidity.

Summer diseases and insects

Although some apple cultivars have resistance to apple scab, cedar-apple rust, fire blight and downy mildew, they are still susceptible to summer diseases, such as fly speck and sooty blotch, and to insect pests. Fly speck and sooty blotch occur together on the fruit surface under warm, humid weather conditions. Fly speck is identified by distinct groups of tiny, shiny black spots. Sooty blotch appears as olive green to black smudges. Both of these diseases are superficial blemishes that can usually be removed from the surface of the apple with mild scrubbing. In contrast to the summer diseases, control of insect pests on disease-resistant apple cultivars may require trapping, mating disruption or insecticide application.

Rootstocks

Most of these scab-resistant cultivars are available from nurseries on rootstocks that that produce relative large to very large trees such as M.26, M.7 and MM.111. However, M.26 is very susceptible to fire blight and, therefore, is not recommended for planting in Missouri.

Cedar-apple rust, plant disease that primarily affects eastern red cedar (Juniperus virginiana) and various apple and crabapple species (genus Malus) in North America and that is caused by the fungus Gymnosporangium juniperi-virginianae. Both hosts, the junipers and the apples, are required for completion of the rust fungus’s two-year life cycle. The disease can be controlled by eradicating either host in a given area or by timely application of a fungicide, in spring for junipers and in summer for apples. Cedar-quince rust, caused by G. clavipes, and cedar-hawthorn rust, due to G. globosum, are similar diseases that infect junipers and various members of the rose family.

cedar-apple rustInfection of cedar-apple rust, a fungal disease, on an eastern red cedar (Juniperus virginiana). The disease affects both juniper and apple species. John H. Gerard

Infection in eastern red cedars and other junipers is marked by the presence of greenish-brown to chocolate-brown galls, known as cedar apples, on the twigs and young branches. The galls are round to kidney-shaped, are up to 5 cm (2 inches) in diameter, and are covered with jellylike yellow to orange-brown spore horns in rainy spring weather. A single gall may produce several billion spores, which are carried by the wind to infect apples and crabapples. Pale yellow to orange-yellow spots with sticky centres and minute black pycnia (fruiting bodies) form on the young leaves and fruit. Orange tubelike structures known as aecia later develop on the undersides of leaves and on fruits, which drop early. In late summer, the aeciospores of those structures are carried by the wind to junipers; the resulting galls do not produce spores until the second spring.

cedar-apple rustOrange spots symptomatic of cedar-apple rust, a fungal disease, on an apple leaf (Malus species). Lee Reich/AP Images

My crabapple tree is dropping leaves like crazy! Almost half the foliage is gone and the remaining leaves have orangish-spots.

Cedar-apple rust is a disease that causes substantial injury to apple, crabapple and hawthorn trees in Nebraska. Trees severely defoliated by the disease are a common site in late summer. Infection of trees, by the fungal spores that cause the disease, begins when the flower blossoms are pink but before they have opened, usually May and June. The fungal spores are released at this time by their alternate host, juniper. The spores are blown by wind to susceptible apple trees and soon leaf spots develop.

Leaf spots caused by cedar-apple rust are bright yellowish-orange in color and vary in size. The spots may have a band of red or yellow around them depending on the tree’s susceptibility to the fungus. Fruit symptoms are similar to leaf symptoms. Infection of the fruit occurs near the underside, blossom end of the fruit and the spots are yellowish-orange in color.

The most effective method control for this disease is to plant resistant varieties of apple, crabapple and hawthorn. Unfortunately some very popular older varieties of apple and crabapple, which are still commonly found in our landscapes, are susceptible to cedar-apple rust and must be sprayed annually to control the disease. Injury to the apple trees occurs when extensive infection leads to premature leaf loss. Repeated infection for several growing seasons will weaken the tree and may result in decreased fruit production and death.

Susceptible trees need to be sprayed regularly during the period just before the blossoms open, or the early pink bud stage. Several additional fungicide applications should be made at 7-10 day intervals to provide good protection. Apple trees can be treated with several fungicides during this time, although Funginex (triforine) is the preferred product. As always, follow the label directions carefully, especially if this is an apple tree from which you plan to harvest fruit.

Resistant cultivars of apple include Granny Smith, Red Delicious, Early MacIntosh, Freedon, Liberty, Northwestern Greening, Nova Easygrow, Priscilla, Redfree, Sharon and Sir Prize. Resistant cultivars of crabapple include Bob White, Donald Wyman, Indian Magic, Prairifire, Red Jade, Sugar Tyme, and Zumi Calocarpa. Resistant hawthornes include Crataegus crus-galli, C. intricata, C. laevigata ‘Autumn Glory’, C. phaenopyrum, C. pruinosa and C. virdis.

More information:
Cedar-apple and Related Rusts of Apple and Ornamentals, University of Nebraska- Lincoln Extension

Watch out for rust that can jump from incense cedars to fruit trees

CORVALLIS, Ore. – Are globs of bright orange goo attacking both your incense cedar and pear trees?

You could be dealing with a potentially devastating fungus known as Pacific coast pear rust.

“On cedar trees, it looks like someone threw orange marmalade all over the tree,” said Jay Pscheidt, plant pathologist with the Oregon State University Extension Service. “It typically cycles from incense cedars to hosts in the rose family in early springtime, around the time that pears go through bud break.”

The fungus, also known as Gymnosporangium libocedri, must reproduce using two hosts — making its life cycle unique, Pscheidt said.

Its life cycle begins on incense cedar, which is not initially infected with the disease but carries it for three years. Bright orange goo with a jelly-like texture weighs down branches and produces airborne spores that float to nearby pear trees. These spores infect fruit and sometimes even green shoots and leaves.

Then those spores float back to the cedar and infect it with the same fungus, but now called a different name — “cedar broom rust.”

Pacific coast pear rust can thrive on any plant in the rose family. This includes the trees crabapple, hawthorn and mountain ash, as well as apple. It also includes the shrubs quince, serviceberry and wild roses.

Cedar rust can affect plants in western and southern Oregon. Since incense cedar is not widespread in the eastern and central parts of the state, it is not as much of a problem there.

“Wet weather is more favorable for rust diseases, and we saw a ton of it last year because it was so rainy in the spring,” Pscheidt said. “So far this year it’s a medium-level problem.”

The rust is not harmful to humans, but it deforms fruit and reduces yield. Cedar trees and rosaceous plants with numerous infections can decline and may die. Symptoms are most obvious in May.

A gardener’s best defense is to identify the rust’s alternate hosts, then remove the species from nearby areas permanently, Pscheidt said.

Spores can survive on cedar for three years, while living only for one year on rosaceous plants. New spores attack rosaceous plants annually.

There are no pesticide products available for home use to control the disease on incense cedars, according to Pscheidt. Gardeners can spray the pesticide known as Immunox on flowering pears.

The Pacific Northwest Plant Disease Management Handbook offers guides to Pacific coast pear rust and incense cedar rust.

Cedar apple rust is caused by Gymnosporangium juniperi-virginianae, a fungus that needs both a cypress-related evergreen plant and an apple-related plant to complete its lifecycle. Incidence and severity of the disease varies from year to year and is more prevalent in very wet springs and very humid summers. If you have both host plant types in your yard and find symptoms on one, you should look for symptoms on the other as well. There are related rusts on quince, hawthorne and serviceberry for which you can follow these guidelines.

SYMPTOMS

Junipers: Junipers, cedars, and arborvitae are evergreen hosts for cedar apple rust. Eastern Red Cedar is the most common. The disease is more of a health threat to them than to apples because the lesions can strangle and kill infected branches. Even so, cedar apple rust is not considered life-threatening for its evergreen hosts. They are infected in late summer and autumn and form greenish brown or rusty brown galls as small as 1/16” or as large as 2”. Most people notice a gall when it swells during spring rains and becomes a bright orange gelatinous mass perhaps 1” to 3” wide, sometimes with tentacles that make it look as if “it came from outer space”. This mass produces spores that can travel long distances but usually infect apples within a few hundred feet. Broad junipers in the chinensis family (such as ‘Pfitzeriana’) and horizontalis groundcover junipers (such as ‘Wiltonii’) may be somewhat cedar apple rust resistant. Narrow uprights may be more susceptible.

Apples: On apples, cedar apple rust is generally an appearance issue rather than a life threatening disease. An untreated infected apple tree can stand defoliation year after year, although eventually it will be weakened and may eventually succumb to other pests. Apple trees are infected in the spring when spores from the juniper hosts land on new leaves. The home owner usually doesn’t notice the spots created by infection until the fungus is advanced to its next reproductive stage in midsummer. Spots enlarge and often develop a distinctive red band around the circumference. Eventually the underside of the spot will develop spidery fingers about 1/8” long that produce new spores to infect host junipers. Some apple cultivars are slightly more resistant and have smaller or fewer lesions. Among the crabapples Malus ‘Adams’, ‘Donald Wyman’, ‘Prairifire’, ‘Profusion’, ‘Snowdrift’, and ‘Sugartyme’; M. floribunda; M. sargentii and its cultivar ‘Tina’; and M. x zumi var. calocarpa are somewhat resistant. Among orchard apples ‘Baldwin’, ‘Cortland’, ‘Gravenstein’, ‘Liberty’, ‘Macintosh’, and ‘Red Delicious’ are somewhat resistant.

TREATMENT

FOR APPLE HOSTS: Once infected, no treatment is effective on the current year’s foliage. Preventative treatment, however, is very effective.

Late Winter: Dormant oil should be applied in the late winter to smother overwintering spores on bark, branches, twigs, and buds.

Spring: A fungicide should be applied following package directions, usually when the flower buds turn pink, again when the petals have fallen, and once more about 10 days later. A light spray on the soil below the plant might help as well.

Fall: Thorough clean-up of all fallen leaves will greatly reduce the source of new spores the following spring. Get the leaves off your property if at all possible rather than putting them in your compost.

FOR EVERGREEN HOSTS: Pruning out lesions is the most effective way to reduce infection. Disinfect pruners between cuts (dip into a solution of 1 quart water with 2 tablespoons bleach). No chemical treatment is completely effective but application of a fungicide may be somewhat effective in reducing lesions.

FUNGICIDES

FOR APPLE HOSTS: Be sure to check if the fungicide you plan to use is safe for food crops. The following are appropriate for food crops.

CAPTAN: Bonide’s Fruit Tree Spray, Ortho’s Home Orchard Spray, Fruit Guard, Captan, Orthocide

CHLOROTHALONIL: Bonide’s Fung-onil Multipurpose Fungicide, Daconil 2787, Ortho’s Multipurpose Fungicide

FERBAM: Carbamate 76WP, Ferbam; use in early spring since it leaves an unsightly residue

MANCOZEB: Dithane DF, Dithane M45, Manzate, Mancozeb Flowable

MYCLOBUTANIL: Spectracide IMMUNOX

FOR EVERGREEN HOSTS ONLY: You may use any of the above fungicides on an evergreen host as well as those listed below. PLEASE NOTE, the following fungicides are NOT appropriate for food crops.

DIMETHYL 4,4-o-PHENYLENEBIS: Bonomyl

PROPICONAZOLE: Bonide’s Fung-onil Lawn & Garden Disease Control, Ortho’s Lawn Disease Control, Banner

TRIADIMEFON: Bayleton

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