Airborne rust spore lands on daylily leaf
Spore germinates and fungus enters leaf through stoma (small pore in leaf)
Mycelium (the body of the fungus) grows inside leaf and feeds on nutrients within plant cells
Mycelium eventually produces new spores below leaf surface
Leaf surface ruptures, releasing new spores into the environment
New spores re-start the cycle

This animation illustrates the asexual cycle involving urediniospores ("summer" or "repeating" spores) which occurs on daylilies alone and can be repeated indefinitely while conditions are favourable.  The complete life cycle of daylily rust includes a sexual stage and involves another plant, Patrinia. For a more detailed explanation of the asexual cycle shown above, click here.  For a detailed description of the full life cycle including the sexual stage, click here.  To see an animated version of the complete life cycle, click here.