Leaf Rusts of Hardwoods and Needle Rusts of Conifers
Juniper Broom Rust - Gymnosporangium nidus-avis
Juniper with witches' broom.
In the spring telia start to form directly out of the branches on the broom.
Dried telia (dark areas) on the branches. Note the pointed needles of the juniper broom. The rust induces juvenile needles to form which are sharp pointed needles in contrast to the smooth rounded mature needles found on the other areas of the tree.
When wet, the telia expand into a jelly like matrix.
The telia contain teliospores that will produce basidiospores.
Serviceberry, Amelanchier, is the alternate host for Juniper Broom Rust.
Pycnia are produced on top surface of Amelanchier leaves.
Aecia are produced on the bottom of Amelanchier leaf. The aeciospores infect junipers
Fir-Broom Rust
Melampsorella causes a witches' broom on fir. The alternate host is chickweed.
Pycnia and aecia are produced on needles of the broom on balsam fir.
A view through the stereoscope showing a needle with pycnia (black dots) and aecia (white structures that produce aeciospores).
Chickweed with uredinia. Telia will form later in the summer
_____________________________________________________________________
Spruce Broom Rust and Spruce Needle Rust - Chrysomyxa species
Witches broom on spruce. Pycnia and aecia form on the needles. The alternate host is bearberry (also called kinnickinnick) that has the uredinia and telia.
Some species of Chrysomyxa attack spruce needles but do not form witches brooms. Pycnia and aecia form on the new needles. The alternate host is labrador tea where the uredinia and telia form.
Spruce needle rust can produce loads of aeciospores.