Gymnosporangium rusts

Rust diseases on woody ornamental plants are caused by several fungal genera with Gymnosporangium being one of the most common. These fungi require two alternating hosts to complete their life cycle. They infect conifers, mainly Juniperus species such as eastern red cedar, and woody plants in the Rosaceae family such as apple, quince, mountain ash, crabapple, pear, hawthorn, serviceberry, and rowan. On rosaceous hosts, Gymnosporangium rusts are characterized by leaf spots, defoliation, twig galls and fruit blight.