Cedar/Apple Rust
Cedar/apple rust is a fungus that spends its life moving back and
forth between apple and crabapple trees and red cedar trees. The disease
does not significantly affect the health of the red cedar. However, the
yield of apple trees will be substantially reduced, and yearly infections
will reduce the vigor of the trees.
The disease is easily identified on the upper surface of the leaves by the bright yellow lesions. The spots enlarge and turn orange, then develop black spots. Small tubes will appear on the underside of the leaf late in the Summer. The fungus will form brown to reddish-brown galls on the red cedar. Bright orange, gelatinous spore horns will protrude from the gall during wet, warm Springs. Control on the cedar is to simply trim off any galls when they are found.
To control cedar/apple rust on apples and crabapples, a spray program using a fungicide labeled for that purpose is necessary. The trees must be treated before they become infected. Repeated applications are necessary because the infecting spores are produced over a long period of time. Be sure to read and follow all label directions.
A good way to avoid the problem altogether is to plant resistant varieties of apples and crabapples. The fungus is also found on Serviceberry, Mountian Ash, and Hawthorne.
Revised: 03/10/98
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