What is Cedar Apple Rust?


Cedar Apple Rust Pucciniaceae (Gymnosporangium juniperivirginianae)

Yikes!! Sounds ominous, no? Eh, not really. More of a manageable nuisance. 

In this article we will discuss what is Cedar Apple Rust, how to prevent it, how to treat it and is it harmful to humans, pets, wildlife, other plants and are the apple edible. 

Let's face it, we love our apple trees. Nothing is more frustrating than planting our favorite apple trees, nurturing them, taking care to precisely prune them,  babying them to sweet delicious fruit bearing maturity, only to come out one summer morning to find them suffering from pests, fungus or disease. Blech! Luckily Cedar Apple Rust isn't the worst of the worst. Let's take a look.  

What is Apple Cedar Rust?

Cedar apple rust is a member of the family Pucciniaceae (Gymnosporangium juniperivirginianae), a group of fungi that contains many species that usually require two or more hosts to complete the life cycle. Members of this family are known as rusts because they are orange or reddish in color. It is primarily a disease of apples and crabapples. The fungus causing cedar-apple rust lives nearly two years on juniper, the primary host. From July to September, spores from apples fall on junipers. During warm, moist weather, the spores germinate and infect twigs. Small galls become apparent on juniper the next spring and grow during the summer. Even small galls can produce millions of spores. 

Note:  Although apples may occasionally become infected by spores produced several miles away (up to two miles), most infections result from spores produced on Juniperus within a few hundred feet from the apple trees. Once infected, no treatment is effective on the current year’s foliage. 


Early Stages of Cedar Apple Rust: On apples and crabapples the circular, yellow lesions will appear on the upper surfaces of the leaves, shortly after they bloom. Heavy rains within the first two weeks of breaking bud and leaf development can increase the severity of the disease.

Late Stages Cedar Apple Rust: In late summer, this area will produce the orange and brown rust-colored spores.

Underside Apple Leaf: As the disease progresses, the undersides of the leaves below the yellow spots will develop raised orange structures that will ooze from the center, turn black, and appear as black dots. Severely infected leaves may drop prematurely, especially during a dry summer. 


Is It Harmful?
Cedar Apple Rust is not harmful to people, pets and wildlife. The fungus does not typically kill or harm trees and surrounding plants or other fruit producing plants and trees. If fungus sets in on small young twigs, it can disfigure them, pruning those young branches removes the disfigured branches. If not treated, the fungus can reduce crop production. We don't recommend eating the apples, however, they are harmless. 

Treatment: In 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. Fungicides used should be specifically labeled for use on apples. Fungicide sprays will protect young foliage from infection during the time the galls on the junipers. Pesticides registered for use include captan, chlorothalonil (Daconil), copper, mancozeb, maneb, sulfur, thiophanate methyl (Cleary 3336), thiram, triadimefon, and ziram. Preventive works the best. 
In the fall, thorough clean up of all fallen leaves, this will greatly reduce the source of new spores in the next year. Completely remove the leaves from your property, burning them works well. Do not compost. 
Care: Destroy nearby wild, abandoned or older apple tree, crabapples, cedars or junipers. If only a few “cedar-apples” are present, prune and destroy them. 
Apple Varieties Known To Be Disease Resistant: 
Red Delicious, McIntosh, Arkansas Black, Winesap, Mollies Delicious, Spartan, Priscilla, Liberty and Empire
Apple Varieties That Are Susceptible: 
Prima, Sir Prize, Lodi, Jonathan, Rome, Golden, Delicious and Jonafree. 
Crabapple Varieties Known To Be Resistant:  Malus ‘Adams’, ‘Donald Wyman’, ‘Prairifire’, ‘Profusion’, ‘Snowdrift’, and ‘Sugartyme’; M. floribunda; M. sargentii and its cultivar ‘Tina’; and M. x zumi var.
Crabapple Varieties Known To Be Susceptible: 

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  • Charlie Winter
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