Many of you may think there is nothing to say on this topic. I would agree that traditionally we see few dis-ease problems on daylilies. The fungal host index, Fungi on Plants and Plant Products in the United States, reports many diseases on daylily; but few cause problems to plant growth. A "new" disease has appeared on this host in the last 2 years and has caused quite a stir among producers and home growers alike. First, however, I mention some more common diseases you could confuse with it.
We occasionally see an anthracnose caused by the fungus Colletotrichum (like that on hosta and other perennials). It is associated with leaf scorch and can occur on stems. Usually we see this fungus on injured tissue in hot, humid weather. It has not caused many problems on daylily and does not move to healthy tissue. Look for bleached, brown, or scorched tissue on the leaves, with small (pinhead-sized) masses of clear to yellowish spores (use a hand lens).
A more common disease on daylily is leaf streak. Two fungi are associated with this disease: Collecephalus or Gloeocephalus. This disease occurs as yellowing along the central vein of the leaf. Small reddish brown, elongated spots appear in the yellowed areas. Often the brown spots are surrounded by yellow. This disease can be confused with rust, but there are no pustules or rusty spores. Daylily cultivars vary in susceptibility to streak, but generally the most severe result is streaking and death of infected leaves. To avoid spread of this disease, try to irrigate the soil rather than the foliage and avoid working with wet plants. Keep plants thinned to provide better air movement. No fungicides are listed specifically for this purpose, but general-use fungicides could work as preventives where this is a chronic problem.
The new disease on daylily is rust, caused by Puccinia hemerocallidis. It has been reported in the United States for 2 years. The fungus is native to Asia, with a natural range similar to that of daylily species. Due to much hybridizing of daylily, the disease resistance that occurs as plants evolve in nature has been lost. Cultivars reported as susceptible include Attribution, Pardon Me, Gertrude Condon, Crystal Tide, Colonel Scarborough, Starstruck, Joan Senior, Imperial Guard, Double Buttercup, and Stella De Oro.
What do you look for? This looks like most rust diseases. We see uredinial--telial stages on daylily. Look for raised pustules on either surface of the leaf but especially the undersides. The yellow-orange to reddish brown pustules produce abundant spores that rub off when touched. Resistant varieties may produce only yellow flecks. A few Web sites discuss this rust and show pictures of the disease and pathogen. A site to start with is ncf.ca/~ah748/rust. html.
The big concern over this disease is that it spreads very rapidly (new infections arise in 2 to 3 days on more susceptible cultivars), and daylilies have become one of the most popular and widespread perennials in the Midwest. Does it kill entire plants? We do not believe so, but it may kill infected foliage on susceptible plants. If found, infected foliage should be removed and fungicides considered to protect new foliage. State and national plant inspectors are watching for this disease, but you should too.
If you think you have rust on your daylily, get confirmation from a plant pathologist. Send a sample to a clinic or work with your Extension educator. Get the facts before you remove plant tissue and spray chemicals. For details on how to send a sample to our clinic, consult issue no. 2 of this newsletter.