Pucciniastrum goeppertianum on Blueberry (Vaccinium sp)
This deformity on highbush blueberry is called Witch's Broom. It's caused by a fungus, Pucciniastrum goeppertianum. The fungus spends part of its life cycle on balsam fir (Abies balsamea). When the fungus releases its spores, if they land on the stems or leaves of blueberry, the bush then becomes infected. The fungus overwinters on the bush and releases spores in the spring, which will infect more balsam fir trees, starting the cycle again.
Habitat: Highbush blueberry in a mixed forest