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Cedar Rust diseases PDF Print E-mail
Thursday, June 06, 2013 12:23 AM


OSU-Extension Paulding County

Ag Educator


With the spring rain comes the time for the Juniper to flower. From a distance it looks as if the blooms are large and orange. Yet wait a minute. Doesn’t the juniper produce cones? On closer inspection, unease turns to horror. Large, alien looking, carroty gelatinous tentacles seem to have sprung up all over the tree. This is a cedar rust fungal disease.

There are a number of “cedar rust” diseases in which the fungus alternates its life cycle on two plant hosts; one host plant is the cedar or juniper species and the second host can be an apple, crabapple, or hawthorn. In many cases these diseases are minor problems, although the orange colored fungal structures produced are highly visible in the landscape.

One of the cedar rust diseases is called “Cedar-Apple Rust.” The gelatinous stage of cedar apple rust occurs in the spring. Most of the year, the cedar stage of the fungi will appear as a growth the size of a golf ball on the branches. The galls really do not harm the cedar tree and will drop off after a couple of years. These galls are not very noticeable except when they “bloom” in the spring and it does not really harm the cedar trees.

For the rest of the year, the cycle is spent on apple trees. On the apple trees, the disease does cause damage to the foliage and the fruit. The damage shows up as blotches on the leaves and on the skin of the apple fruit. Symptoms of the Cedar-Apple Rust on flowering crab and apple trees are easily identified. In late spring or early summer, bright, yellow-orange spots approximately 1/8 to 1/4 inch in diameter form on the upper surface of the leaves. These spots gradually enlarge and turn orange.

Leaves with numerous spots drop during the summer. Premature defoliation weakens the tree and reduces fruit set and yield the following year. Trees with severe defoliation also are susceptible to other diseases. Cedar-Apple Rust may cause fruit lesions. Diseased fruits develop deep pits or become distorted and usually drop before harvest.

Removing and disposing of the orange galls will improve the appearance of the red cedar and reduce the spores that would in turn infect apple trees. There is no need for fungicidal sprays on cedar. The best way to control the fungus on apples is with timely applications of the proper fungicide.


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