Fir witches' broom

The causal agent of this disease is the rust fungus Melampsorella caryophyllacearum. This specialized parasite primarily affects various species of fir, causing specific structural changes in the shoots known in forestry as «witches' brooms».

The disease affects different fir species, including Siberian, Caucasian, and European fir. The fungus utilizes plants of the Caryophyllaceae family, such as chickweed and stitchwort, as intermediate hosts to complete its life cycle.

The primary symptom of infection is the emergence of dense, irregularly growing shoots that form thick, bush-like clusters called «witches' brooms». At the attachment points on trunks and branches, galls, cankers, and cracks often form, leading to significant deformation of the tree.

High air humidity and moderate temperatures, typical of coniferous forests, favor the development of the fungus. Spores are dispersed by wind from intermediate hosts to fir needles, where infection of young tissues occurs during the active shoot growth period.

The harmfulness of the disease lies in a substantial reduction of tree growth, weakened immunity, and premature branch dieback. Where «witches' brooms» develop, the wood becomes brittle, increasing the risk of windthrow and infestation by secondary pests such as bark beetles.

Control measures include sanitation logging of infected trees to reduce the inoculum level within forest stands. It is also recommended to promptly remove weed vegetation of the Caryophyllaceae family in forest nurseries to prevent the spread of spores to young seedlings.