The following is information on daylily rust, a relatively new introduced disease that can attack daylilies.
The recent introduction of a new disease has complicated the nearly trouble-free reputation of daylilies. Daylily rust, caused by the fungus Puccinia hemerocallidis, produces yellow spots or streaks on leaves and scapes, with raised pustules commonly on the undersurface releasing infectious orange spores. The frequently seen Daylily Leaf Streak, caused by the fungus Aureobasidium microstictum, begins with water-soaked brown spots usually beginning at the top of the leaf. As these work their way downward, they lengthen into brown streaks with yellow borders. A quick way to confirm Daylily Rust as the problem is to wipe a clean white tissue over the leaf lower surface – an orange stain indicates the presence of the rust spores. A severe infection on susceptible varieties may result in withering and death of the leaves, but the crown and roots are not involved.
As with other rusts, P. hemerocallidis has a life cycle that features two hosts, though it requires only the daylily to survive asexually from year to year. On daylily, the fungus produces two kinds of infectious spores – the orange urediospores, spreading disease during the growing season to other daylilies, and the darker, thicker-walled teliospores. These can survive the winter and infect the alternate host to complete the life cycle with the sexual stage. The alternate host is Patrinia, a perennial with fern-like leaves and bright yellow umbels, sometimes used as a filler for border plantings. No infection of Patrinia has been observed in the US, however, and the fungus can infect other daylilies without infecting the alternate host. Reports that Hosta can act as an alternate host have not been verified.
On daylily, disease spread is favored by warm temperatures and high humidity. Cloudy rainy weather is best. Poor air circulation and overhead watering at night should be avoided. Spores can spread by wind, windblown rain, or mechanical transfer by clothing or tools, for example.
Management: Select varieties that are more resistant.
The following list is from the Texas Cooperative Extension, Texas A & M University, April, 2004. Destroy infected leaves and those of nearby plants.
Remove shoots as close to the ground as possible. Fungicide sprays can be used when new growth emerges. In the fall, remove foliage from all plants and destroy or compost these (hot compost temperatures will eradicate the urediospores). If you are planting newly purchased daylilies in the spring, prune them back to remove possible inoculum from your landscape. Fungicides available to commercial growers for managing this disease include azoxystrobin (Heritage), propiconazole (Banner Maxx), myclobutanil (Systhane), thiophanate methyl (Cleary’s 3336 and others) or flutolanil (Contrast). Follow all label directions.
Reprinted from an article by Penny Wolkow in the July 10, 2009 edition of the TPM/IPM Weekly Report for Arborists, Landscape Managers & Nursery Managers from the University of Maryland Cooperative Extension http://www.ipmnet.umd.edu/09Jul10L.pdf