Melampsorella caryophyllacearum

The fungus causes witches' brooms, that is, an excessive proliferation of twigs from a single point on a branch. Fir broom rust is rarely fatal, but it can result in growth reduction. The fungus lives on two hosts: the primary host is balsam fir and the secondary host is chickweed. The first type of spores is produced in spring on the two faces of needles contained in the broom. Infected needles are stunted and yellowish-green in colour. The spores form on fruiting bodies that look like small, round.. more