What is daylily rust?
Daylily rust is a fungus with a complex life cycle. In the course of that life cycle, the rust switches from parasitizing daylilies to a briefly free-living form to parasitizing another plant called Patrinia, and then back to daylilies. Along the way, it changes from uninucleate to binucleate and back again and produces five distinct types of spores. The stage of greatest concern to us now, as daylily growers, is the stage that infects and reinfects daylilies through cloned spores called urediniospores. These can be spread by wind, splash, contact, and animal (or human) transport. When they arrive on a leaf, under the right conditions of temperature and humidity they will germinate and attempt to grow through a stomate to infect the interior tissues of the leaf. When enough growth has been achieved inside the leaf, and environmental conditions are right, the rust fungus produces pustules that burst through the surface of the leaf to release a new generation of cloned spores.
