The Richmond Register

May 14, 2013

Cedar rust may cause serious apple loss


Extension Agent

RICHMOND — If you have cedar trees in your landscape it may be a good time to go look at them. You may notice a large orange mass with projections all over it.

Aliens have not landed, so do not be alarmed! It is just one stage of the fungus called Cedar Apple Rust.

Spores from this disease overwinter for multiple years on cedar trees as small galls. These galls begin as light brown to reddish or chocolate brown in color. They are sometimes called “cedar apples,” and can range from pea-sized to 2 inches in diameter.

Rainy weather encourages the galls to slowly enlarge and produce long projections called “horns” in the spring. The horns are actually columns of fungal spores. So the orange mass you see now has been slowly developing on your tree for a few years.

The fungal mass’s emergence in spring occurs around the same time that apple trees are beginning to bloom. The spores from these galls are carried by the wind to the blooms on the apples trees. Spots begin forming on the top portion of the leaf about 10 to 14 days after the infection has occurred. The spots on the leaves continue to grow until they form spores. The spores from the apple tree are blown to the cedars and the whole cycle begins again.

Although cedar rusts can cause unsightly growths on evergreens, they do not usually cause serious damage to these plants. Rust diseases can cause serious losses on apples, however, as a result of both fruit and leaf infections.

Infected fruits can drop prematurely or have a reduced commercial value if they remain on the tree through harvest.

Leaf infections often result in premature leaf loss, which reduces the size and quality of the that season’s fruit crop, weakens the tree, and may cause a reduction in bloom the following year.

Trees allowed to become heavily infected for several years become stunted, are increasingly susceptible to winter injury, and might eventually fail to produce fruit.

So what can we do to help our apple trees?

Destroy any nearby cedars, at least within one hundred feet of the apple tree.

While the spores have been shown to travel from miles away, removing the closest cedars will decrease the likelihood of this disease.

Scout your cedars in the winter and destroy the horned galls that form.

Do your homework before you buy trees. Purchase apple trees that are disease resistance.

As a final resort, there are fungicide sprays which can be effective if properly applied beginning prior to bloom.

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