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Black witches broom (Apiosporina collinsii)  Helen Atthowe, Missoula County Extension
 HOSTS: Various species of serviceberry (Amelanchier). DESCRIPTION:
Apiosporina collinsii
produces perennial mycelium in branches and fruiting bodies on leaf
surfaces. Mycelium grows mainly toward the tip of the twig and enters
buds, petioles, leaf blades, and flowers. As additional shoots
develop
in the leaves, the fungus grows into new tissue and causes development
of abnormally short, thick and numerous twigs. On shaded
branches,
infection is swollen and bent toward the ground. Diseased
branches in
open areas develop loose brooms. Many
twigs in brooms die back during winter. Leaves on a broom are
dwarfed
and yellow. Branches that have brooms become less vigorous but
will
not die from the parasite. The disease has little net effect on
the
plant unless brooms are numerous.
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