Cedar Hawthorn Rust

(Gymnosporangium juniperi-virginiana) - Cedar hawthorn rust is caused by a fungal pathogen, Gymnosporangium juniperi-virginianae. This fungus must spend a phase of its life cycle on both the red cedar and apple (or crabapple tree). Gymnosporangium form galls on the cedar. Typically these galls grow on the cedar for 2 years. In the spring, matured galls will produce bright orange soft tendrils, known as telial horns or spore horns. Spores formed on the cedar are transmitted to the apple tree via air currents. After disease occurs on the apple tree for a period of time, small whitish paper-like tubular projections can appear on the underside of leaves or on the fruit. These structures are called aecia and will produce spores that will infect the red cedar and form new galls. These spores will not reinfect apples.

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