Daylily rust, caused by Puccinia hemerocallidis, was first reported in the United States in 2000; it is thought to have been brought on plants from Costa Rica. The disease quickly spread in 2001, appearing in most of the eastern half of the United States. It drew much publicity that year. The disease was discussed in issues 15 and 20 of the 2001 newsletter. Symptoms include various spots and streaks on foliage, from pale yellow to brown. Within these spots and streaks, you find rust pustules on either the upper or lower leaf surface. Spores are yellow-orange to reddish brown and wipe off when rubbed. You can see these easily with a hand lens.
According to the scientific literature, this rust fungus has multiple hosts. The uredial/telial stages of the fungus are reported on daylily and hosta. Fortunately, the rust has not been found on hosta in the United States. The aecial host reported in scientific literature is Patrinia, but that host has not been reported in the United States either. The fungal stage found on daylily is the repeating stage: It can repeatedly reinfect daylily without an alternate host.
The good news is that daylily rust has not shown an ability to overwinter in Illinois. There really are some advantages to our cold winters! One of the first reporters of daylily rust is Jean Williams-Woodward, a Georgia plant pathologist. She said that rust did not overwinter and return after the winter of 2001 even in her Georgia gardens.
If you manage to bring daylily rust to your garden in Illinois, it quickly spreads to other daylilies by wind and air currents. Spores need only 4 hours of nearly 100% humidity and moderate temperatures to germinate, so infection is rapid. Still, the fungus dies in the winter, and it does not kill your plants. Keep these facts in mind when choosing management options.
Most Illinois daylily rust cases we have seen were bought with mail-order plants. Williams-Woodward suggests treating mail-order plants as follows. Remove all leaves except the central bud. Soak the plant for 10 minutes in 10% Clorox before planting. As an extra precaution, isolate new plants until new leaves emerge free of rust. You can also stop planting susceptible cultivars. Research on varietal resistance is under way. A study in Arkansas is described at http://daylilies.uaex.edu/.
If you choose to use fungicides, there are many choices. Chemical options are available to protect new leaves from infection, but a strict spray program of 7 to 14 days all summer is needed to keep the disease at bay. Homeowners often see success with chlorothalonil and mancozeb, which are protectant-contact chemicals. At least two systemic products packaged for homeowners work against rusts--propaconizole (Fertilome Systemic) or myclobutanil (Immunox). Commercial growers usually use systemic products such as myclobutanil (Systhane), triadimefon (Bayleton, Strike), propaconizole (Banner Maxx), azoxystrobin (Heritage), and flutolanil (Contrast, Prostar). Refer to issue 20, 2001, for details on chemical concerns.