EXTENSION PLANT PATHOLOGY, EXTENSION HALL, AUBURN UNIVERSITY, AL 36849-5624 July 3, 2001 PP-506 Identification and Control of Daylily Rust Austin Hagan (firstname.lastname@example.org) Extension Plant Pathologist and Professor Department of Entomology and Plant Pathology A new disease of daylily (Hemerocallis sp.) called daylily rust was found at retail outlets last summer in Alabama, Florida, Georgia, and South Carolina. According to the National Plant Board (www.aphis.usda.gov/npb/daylily.html), daylily rust has also been found in California, Maryland, Minnesota, Mississippi, Tennessee, and Texas. Unfortunately, this disease has already been found at a retail nursery in Mobile and will most likely turn up at other retail locations as the summer progresses. Apparently, diseased daylily plants were imported from Central America, propagated at one or more sites, and then were distributed to stores and retail nurseries across the U.S. Recently, a shipment of diseased daylily sets from Costa Rica was intercepted. Although, the Plant Diagnostic Laboratory in Auburn has received no samples of rust-damaged daylily, it's safe to say that this disease has already been introduced into Alabama landscapes. The daylily fungus Puccinia hemerocallidis is a heteroecious rust, which requires two different host plants (daylily and the herbaceous perennial Patrina sp.) to complete its life cycle. Like many other rust fungi, however, spores (uredospores) produced on daylily are infectious to other daylily. In other words, this disease probably will spread from newly established diseased plants to nearby healthy daylily. No information is available concerning the possible long- distance spread of this disease via airborne uredospores. The uredospores of other rust (Puccinia) fungi, especially those on forage grasses and small grains, are often spread long distances by upper air currents. It is not clearly known is whether or not the uredospores can survive the winter on leaf debris and then infect the new spring growth. Since the daylily rust fungus is native to China, Taiwan, Japan, Russia, and Ryukyu Islands (Okinawa), there's a good chance that the uredospores will remain viable from one growing season to the next. From the images that I have seen, symptoms of daylily rust are similar to those of rust diseases on forage and lawn grasses. The first symptoms on the leaves are light yellow, water- soaked spots. Rust pustules, which appear 7 to 14 days after infection, are randomly scattered across the upper and lower leaf surfaces. The spore (uredospore) masses are bright orange in color. The powdery, orange spores will cling to fingers and clothes. Badly rusted leaves will eventually yellow, whither, and die. Some daylily cultivars particularly 'Pardon Me' are so susceptible to rust that all of the leaves are covered with pustules and quickly die. Good images of daylily rust symptoms can be found at the University of Georgia CES web site (www.ces.uga.edu/Agriculture/plantpath/daylilyrust.html). Daylily leaf streak, which is caused by the fungus Kabatiella microstictum, is the only other disease whose symptoms may be confused with those of daylily rust. Typical symptoms include long chlorotic and necrotic streaks running along the midvein. Often the tissues surrounding the elongated necrotic lesions turn yellow. Later, reddish-brown oval, elongated spots may appear along the other leaf veins. Eventually, the badly damaged leaves will wither and die. Unlike rust, no bright orange, powdery spore masses are associated with daylily leaf streak. As I previously indicated, daylily cultivars differ considerably in their reaction to daylily rust. If you are like me, however, you differentiate daylily on the basis of their flower color and not by cultivar name. Anyway, the cultivar 'Pardon Me' gets the daylily rust Darwin award. Basically, rust blasts this cultivar. Other susceptible cultivars include 'Gertrude Condon', Starstruck, 'Stella D'Oro' (a popular dwarf type), 'Joan Senior', 'Colonel Scarborough', 'Crystal Tide', 'Imperial Guard', 'Double Buttercup', and 'Attribution'. Recently, two visiting plant pathologists from Tennessee found rust on the cultivars 'Ruby Galore', 'Ruby Red', 'Lemon Yellow', and 'Angel Baby' at a Mobile Garden Center. They also mentioned that 'Simply Pretty', 'Little Paul', and 'Scarlet Orbit' did not have any observable rust pustules on the leaves. However, some plants were collected to see whether symptoms show up at later date. It's probably safe to say that daylily rust is here to stay. An ex-Alabama Plant Inspector mentioned to me that he saw this disease a decade ago. So, who knows how long daylily rust has really been in the U.S? Control of this disease is going to be quite costly, particularly for daylily breeders and producers. The first step involves cutting off and destroying the diseased foliage followed by a strict regime of protective fungicide applications to the new growth. For the commercial breeder or grower, Banner Maxx, Heritage 50W, and Eagle 40W (Systhane 40W) are the fungicides of choice to prevent the development of rust on the new growth. Applications of the above fungicide should be made every 10 to 14 days. Repeated applications of high rates of either Banner Maxx or Eagle 40W may stunt the foliage of daylily and will cause the leaves to be abnormally dark green. The other control option is to simply destroy the diseased plants and start over with healthy sets. Regardless of the option chosen breeders or producers, stock plants will have to be free of symptoms in order to be eligible for a phytosanitary certification that allows the interstate shipment of daylily. Stop sale orders are being issued when plant inspectors find blocks of diseased daylily at nurseries. However, so many little backyard nurseries produce daylily that inspectors are going to have a hard time checking all of them. The herbaceous perennial Patrina sp. is on the production list of some nurseries in the southeast. As many as six selections of this perennial may be available at retail outlets. While the presence of this plant is not essential for the spread and survival of the daylily rust fungus, the sexual reproduction of this rust on Patrinia could result in the development of new, more virulent races of Puccinia hemerocallidis. Needless to say, this minor perennial should never be planted anywhere near daylily. The situation for homeowners and commercial landscapers is really up in the air. I'd suggest keeping an eye out for this disease in your county and alerting the Alabama Department of Agriculture and Industries should daylily rust appear. If possible, send the Plant Diagnostic Laboratory a sample as well. The controls for daylily rust in the landscape are similar to those employed by commercial producers: sanitation and fungicides. Banner Maxx (propiconazole) and Eagle 40W (myclobutanil) are commercial products and are not readily available. However, formulations of both fungicides are marketed thorough retail outlets as Spectracide Immunox (myclobutanil) and ferti-loam System Fungicide (propiconazole). Refer to the product labels for application rates and instructions. When information concerning possible resistant cultivars becomes available, it will be passed on to you.