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Daylily Rust

Daylilies have generally been considered to be care-free, and this is one reason for their extensive use in landscapes. However, diseases such as daylily leaf streak and now, daylily rust pose a threat to the daylily industry. Daylily Rust (Puccinia hemerocallidis) was first found in the US in Georgia and Florida in 2000. Since that time, this rust has been found in 30 other states. Daylily rust is native to Asia and thought to have entered the U.S. on plant material from Central America. The first case of daylily rust has been confirmed in Massachusetts. Growers and sellers of daylilies are strongly advised to purchase disease-free stock plants from reputable growers and to propagate only from healthy specimens to prevent bringing the disease into their production and retail areas.

Symptoms
Rust appears on the leaves as small water-soaked spots. The spots expand and become raised to form a pustule in the center, which releases powdery spores. The spores of daylily rust are bright orange and are produced on both the upper and lower leaf surfaces. These orange spores can be rubbed or blown from the leaf surface. While daylily cultivars will respond differently, the infected leaf often turns yellow first and then the entire leaf becomes necrotic and dries up. So far all infections have been found on the foliage; it is not known whether tuber infections occur.

Daylily rust can easily be seen on the foliage with a 10X hand lens. A good field test to identify it is to wipe suspected pustules with an ordinary white facial tissue. An orange-yellow stain on the tissue will result if the rust is present on the leaves. Daylily rust can easily be confused with other leaf problems, especially leaf streak disease, caused by Aureobasidium microstictum. No orange stain will result on a tissue if the problem is leaf streak disease.

Life Cycle
Like other rust pathogens, daylily rust is an airborne pathogen. The spores are spread from plant to plant by human contact, wind and wind driven rains.

P. hemerocallidis is a heteroecious rust which means that two distinct host plants are required for the completion of the full life cycle. However, on daylily this rust produces urediospores, also known as polycyclic or repeating stage spores and does not require the alternate host for infection. This means that once a daylily plant is infected, the disease can spread rapidly to other daylily plants. The alternate host is the perennial, Patrinia sp. in the Valerianaceae family. Six species of the perennial Patrinia are sold and grown across the U.S. as an ornamental.

Susceptible Varieties
Daylily varieties differ in susceptibility to the rust. In Massachusetts daylily rust was diagnosed on the "Twice as Nice" daylily collection. The cultivars 'Raspberry Candy' and 'All Fired Up' are the two cultivars in this line that have shown the worst symptoms, with other cultivars, such as 'Moonlight Masquerade', showing less severe symptoms. There are fourteen cultivars in this product line. Varieties in other states which have been reported to be affected since 2000 include: Attribution, Gertrude Condon, Crystal Tide, Colonel Scarborough, Starstruck, Joan Senior, Imperial Guard, Double Buttercup and Stella De Oro.Symptoms range from bright yellow spots to streaks. Following inoculation of leaves, infections can appear in as little as two to three days. Not only does the rust have a short incubation period, but it also spreads fairly quickly in nurseries.

Diagnosis and Treatment
Commercial Flower Growers who have plants suspected of rust infection should send samples for confirmation to: Dr. Rob Wick/Bess Dicklow, Floriculture Diagnostic Lab, Rm. 109 Fernald Hall, University of Massachusetts, Amherst, MA 01003. Call prior to sending samples at 413-545-1045. Leaf samples should be placed between paper towels and then placed in a plastic bag before packaging for mailing. The standard diagnostic fee will be charged. Sanitation is very important in managing this disease. REMOVE AND DESTROY ALL INFECTED PLANTS. Treat uninfected plants with an effective fungicide according to label directions. Fungicides with the trade names Banner, Heritage, Contrast and Systhane are registered for rust. Growers are advised to check labels for broad crop clearance before use.

More information Information and photos of daylily rust are available from the following websites:
Daylily Rust - Massachusetts Introduced Pests Outreach Project
Daylily Rust Alert - National Plant Board
http://www.ncf.carleton.ca/~ah748/rust.html
http://www.ceris.purdue.edu/napis/pests/dlr/index.html

References

Clark, R. 2003. Daylily rust alert. Hort Notes 12(14) p 1. Univ. of Mass. Ext.

Giesler, L. 2001. Daylily rust: a new disease in the United States. NebGuide, Univ. of Nebraska-Lincoln Coop.Ext.

Nameth, S. 2001. Daylily rust found in Ohio. Northeast Greenhouse IPM Notes 11(10) p 4. A publication from Cornell and Rutgers Cooperative Extension .

Riedel M. and Kobayashi H. 1999. Control of leaf streak of daylily with the use of resistance and fungicides introduction. Perennial Plant Assoc. Quar. Journal Autumn 1999, p. 11-21

Schubert, T. 2001. New daylily disease has growers on alert. Perennial Plant Assoc. Quar. Journal. Spring 2001, p 57-58.