Cedar Apple Rust
Cedar-apple rust is a both a fruit disease and an ornamental disease. It is caused by Gymnosporangium spp. and can infect most varieties of eastern red cedar and many cultivars of juniper, apple and crabapple. The symptoms on the deciduous hosts are familiar to most growers and landscapers. The leaves have yellow spots on the upper surface. In late summer, brownish clusters of threads or cylindrical tubes appear beneath the yellow leaf spots.
Galls and swellings on the junipers appear about seven months later and form gelatinous masses of spores after about 18 months. The rust disease is very conspicuous on red cedar and junipers during spring, when the galls are covered with the orange-brown, gelatinous masses. Rust spores formed on the gelatinous masses can not infect other junipers. They infect the leaves of deciduous hosts during wet, rainy weather in early spring.
Cedar Apple Rust on "Jonagold" apple tree
Cedar Apple Rust on Eastern Red Cedar