Orange, gelatinous spore producing structures form along the branch of a juniper 'broom' M. Grabowski, UMN Extension |
Gelatinous, orange fungi can now be found on junipers in
Minnesota on rainy days. Cedar apple rust, cedar hawthorn rust, quince rust,and juniper broom rust are caused by a group of related fungi that spend half
of their life on juniper trees and shrubs and the other half infecting members
of the Rosaceae family, including crabapple, serviceberry, and hawthorn. Despite their eye catching symptoms, these
rust fungi do not seriously affect the health of either host plant.
These rust fungi overwinter as infections in woody branches
of junipers. Cedar apple rust and hawthorn rust result in round woody galls.
Juniper broom rust causes a cluster of small branches, or a broom, to form, and
quince rust directly infects the branch. In wet spring weather, these rust fungi come
out of dormancy and produce gelatinous orange spore producing structures on
rainy days. Spores released from these strange orange fungi are carried by wind
and rain to infect nearby crabapple, serviceberry, or hawthorn trees. The orange
fungal structures on juniper can dry out and rehydrate several times in the
spring, releasing spores each time they are wet.
Galls of hawthorn rust and cedar apple rust will die after
releasing spores in the spring. Brooms and branch infections caused by juniper
broom rust or quince rust may survive for many years, releasing new spores each
spring.
Cedar apple rust gall during a dry period. M. Grabowski, UMN Extension |
Although these rust fungi are eye catching, they cause
little damage to either of their hosts. Junipers tolerate galls and branch
infections and only suffer branch dieback when infection is unusually heavy. Crabapple,
hawthorn, and serviceberry trees develop bright orange to red leaf spots, fruit
infections, and rarely infections of green twigs. Leaf spots are limited to the
leaves currently on the tree and will not spread to new leaves throughout the
growing season. Galls, brooms, and branch infections can be pruned out and
buried in the compost pile to reduce infection on nearby trees in the rosaceae
family if desired.
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