A rust fungus and plant pathogen that alternates between junipers, chiefly eastern red cedar, and apples and crabapples. On the juniper it forms woody brown galls that push out bright orange, gelatinous spore horns after warm spring rains; on apple it causes yellow-orange leaf spots and can deform fruit. It cannot spread from apple to apple or from juniper to juniper, only between the two hosts, and the full cycle takes about two years.
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Habitat
Obligate parasite of living plants. Telial stage on junipers, mainly Juniperus virginiana; aecial stage on apple and crabapple (Malus), and other rose-family plants are reported. The two hosts must grow within a few miles of each other; wind carries spores over a radius of several miles. Galls release spores in spring around apple bloom; aeciospores are released from apple leaves mainly in July and August.
Distribution
Native to North America and common in the eastern and central United States wherever eastern red cedar grows near apples or crabapples; extension services from Texas and Oklahoma to Missouri, Illinois, Tennessee and Michigan report it.
Characteristics
Juniper galls: reddish brown to purplish, woody, dimpled, about 6-50 mm across, producing spores only in their second spring. Telial horns: orange to golden, gelatinous and tentacle-like when wet, roughly 10-20 mm long, shrinking to hard rusty threads when dry and swelling again in later spring rains. Apple leaves: yellow spots on the upper surface after infection, enlarging and turning orange, often with red borders and tiny black spermogonia; later, cup-shaped aecia with hairlike tubes form on the underside. Fruit: lesions near the blossom end, causing dwarfing and malformation. Spore stages: teliospores (two-celled, on the horns), basidiospores, spermatia and aeciospores.
