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Extension > Yard and Garden News > Cedar apple rust is active

Monday, May 1, 2017

Cedar apple rust is active

Orange, gelatinous spore producing structures form along the
branch of a juniper 'broom'
M. Grabowski, UMN Extension 
M. Grabowski,  UMN Extension Educator 

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.
Orange fungi emerging from cedar apple rust galls.
M. Grabowski, UMN Extension 

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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