|Galls on cedar (Photo: H.D. Shew)|
|Gall with dry telial horns (Photo: H.D. Shew)|
Apple leaves and fruit are most likely to be infected when they are wet and temperatures range from 46 to 75 F. Yellow to orange spots are produced on the upper surface of the apple leaves one to two weeks after infection. The spots on leaves may be raised or swollen and infected fruit may be slightly distorted. Small black dots within the lesions signal the production of the next spore type, the pycniospores (also called spermatia). One to two months later, fringed cup-shaped structures (aecia) appear on the underside of the apple leaves and these contain aeciospores, yet another spore type.
The aeciospores are windblown to cedar trees in late summer to early fall, where they germinate and infect to produce galls. The galls produce teliospores in the second year after infection, completing the life cycle. G. juniperi-virginianae survives in the gall tissue for only two years. After its second year, the spore producing year, the pathogen dies in the gall tissue. On apples, the pathogen survives only a few months, just long enough to produce the aeciospores that infect cedar trees.
|Symptoms on apple (Photo: E.C. Lookabaugh)|
Check out this cool video of telial horns expanding (Video: Arlene Mendoza-Moran)