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John Fulton

John Fulton
Former County Extension Director

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In The Backyard

Horticulture columns and tips done on a timely basis
Cedar Apple Rust

Cedar Apple Rust

Posted by John Fulton -

Cedar apple rust is caused by a fungus that attacks two different groups of trees. The first group is apples and crabapples, and the second is juniper and eastern red cedar. In order to survive, the fungus must "move" from one group of host to the other.

On juniper or eastern red cedar, small (3/8 to 1 and 3/16 inches in diameter) galls develop throughout the tree on needles and small twigs. When mature, these galls swell considerably and repeatedly produce orange, gelatinous telial horns during rainy spring weather. As spring rains subside, the galls die, which may cause death of the twig from the gall to the tip.

On susceptible crabapples and apples, tiny yellow spots appear on the leaves after infection in the spring. As the spots mature, they become yellow/orange and swollen with a red border, and develop tiny black dots in the center of the lesion. By mid-summer, small cup-like structures with tubes are visible on the undersides of mature leaf lesions. The fungus may also infect fruit and tender twigs of very susceptible crabapple and apple varieties.

The entire life cycle takes about two years, with a year on each host. The apple phase is easily recognized on the leaves and fruit by just about anybody who has grown apples. The teliospore phase on the cedars is quite striking, but is noticed much less frequently. Fungicides in spray programs do a good job of controlling the apple phase, while the cedar phase is best controlled by buying resistant varieties. Some homeowners cut the galls off before they break out into the "orange blob," but the result is the same: you're going to likely lose the tips on those branches.

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