There is nothing that catches the eye so much as a bright orange slimy tentacle-like fungus hanging from a landscape juniper tree. What is that thing? you might ask. The answer is cedar apple rust, one of several Gymnosporangium rust fungi that infect junipers in the state of Minnesota. Gymnosporangium rust fungi are unique in that they spend part of their life infecting juniper trees, causing unusual brightly colored galls, and the other part of their life infecting leaves, fruits, and green stems of trees or shrubs in the Rosaceae family. The Rosaceae family includes crabapples, hawthorns and serviceberry. Different Gymnosporangium rusts infect different trees and shrubs.
On junipers, the cedar apple rust results in brown woody galls that can grow to over an inch in diameter. With wet weather, the galls produce bright orange tentacle like spore producing structures. These release spores that are carried to nearby crabapple or apple trees, later to become bright orange and red leaf spots. Cedar apple rust galls on juniper can dry down and rehydrate multiple times in one spring. With repeat rain events in Minnesota this year, the cedar apple rusts have been putting on a colorful show. The good news is the galls will dry up and die when warm dry weather arrives. Juniper trees are rarely harmed by cedar apple rust galls although gardeners might notice some dieback on branch tips girdled by large galls.
More information about cedar apple rust and other Gymnosporangium rusts can be found on the UMN Extension webpage, including information on how to identify and manage the different diseases on different host plants.