 To survive the winter "Melampsora medusae" remain as teliospores on the dead leaves of the host, coming back in the spring to be spread by the wind as basidiospores, and infecting new conifers.After about two weeks, aeciospores are produced on the coniferous needles.Those spores serve as inoculum for an infection in live trembling aspen and other poplar trees in another two weeks.