This fungal disease of apple, crabapple and
Eastern red cedar is caused by several species of Gymnosporangium. The disease
not only affects Juniperus species including Eastern red cedar (Juniperusvirginiana)
but requires another host plant, apple or crabapple, to complete its life
cycle. This disease spreads from junipers to the apple and then back to
juniper. It can be a severe problem wherever these two are grown together.
Eastern red cedar is the most commonly infected juniper. On juniper, hard, brown, up to 2-inch diameter galls form near
the ends of the branches in the summer. In the spring following a rain, the
galls produce large, orange, gelatin-like tendrils, full of spores, which can
blow a half-mile to infect nearby apple and crabapple trees.
Symptoms that occur on the apple trees appear as yellow spots on
the upper leaf surface. In the late summer, these yellow spots form spores that
are spread to the leaves and twigs of nearby junipers (within 2 miles) to
Select resistant varieties of
apple (such as `Enterprise`, `Pristine`, `Liberty` or `Redfree`) or juniper.
Prune out all galls on the juniper, if possible. Do not plant apple, crabapple
and Eastern red cedar trees in the same area. If disease is severe enough to
warrant control, or a particular specimen plant is affected, select a fungicide
containing mancozeb or propiconazole.