Gymnosporangium Juniperi-virginianae - The Disease Cycle

The Disease Cycle

Understanding of the disease cycle of this rust fungus is necessary for proper identification and control. Cedar apple rust is caused by the fungi Gymnosporangium or more specifically Gymnosporangium juniperi-virginianae that spend part of their life cycles on Eastern Red Cedars growing near orchards. The complex disease cycle of cedar apple rust, alternating between two host plants, was first delineated by Anders Sandøe Ørsted (botanist).

On the eastern seaboard of the United States, at the first warm rain of spring, the spore horns become gelatinous masses and produce their teliospores.

Wind carries the spores to apple leaves at about the time that apple buds are in the pink or early blossom stage. Upon reaching apple buds or leaves, the spores attach themselves to the young leaves, germinate, and enter the leaf or fruit tissues. Infection takes place in as little as four hours under favorable conditions. Yellow lesions develop in one to three weeks.

In July and August, spores from the apple leaves (Aeciospores) are produced. The wind carries the spores back to Eastern Red Cedars, completing the infectious cycle. The spores land on cedar needle bases or in cracks or crevices of twigs. There, they germinate and producing small, green-brown swellings about the size of a pea. Galls do not produce spores until the second spring. However, mature galls usually are present every year. This fungus produces four out of five of the spores known to be produced by the class Urediniomycetes during its life cycle. (Teliospores, Basidiospores, Spermatia, and Aeciospores. The type of spore it does not produce is Urediospores) Rust fungi have a complicated life-cycle with up to five types of spores (each borne on a different type of structure) in its life cycle and often an alternate host, and an "alternate alternate host" as well.