Conifer - Cottonwood rust
Damage, symptoms and biology
Melampsora occidentalis, like the other Melampsora rusts, causes more serious damage to hardwoods than to its conifer hosts.
The aecia and telia of Melampsora occidentalis are macroscopically similar to those of M. albertensis and M. medusa. However, the aeciospores and urediniospores of M. occidentalis are significantly larger.