Daylilies ( Hemerocallis spp. L.) are planted extensively throughout the United States and thousands of varieties have been developed. Once established in a landscape, daylilies require little maintenance, are drought tolerant, have no special pH or fertilization requirements, and are generally disease and insect free. Recently, however two diseases, Daylily Streak and Daylily Rust, have emerged that threaten the daylily industry. Daylily Rust caused by Puccinia hemerocallidis and Daylily Streak caused by Aureobasidium microstictum are easily confused. A quick diagnostic test is to run your finger along the underside of leaf lesions; an orange, powdery residue will result from the spores of Daylily Rust.
Initial symptoms of Daylily Streak are a central, yellow streak along the leaf midvein that often starts at the leaf tips and progresses downward. This initial streak is followed by necrosis both in the surrounding green tissue and the yellow streak itself. Small reddish brown flecks and oval, elongated necrotic lesions develop on infected foliage. Diseased foliage may wither and die completely. Daylily streak can be avoided by purchasing disease-free stock plants and propagating only from healthy plants. Cultivars differ in their susceptibility to this disease; proper selection of varieties can potentially limit this disease. Daylily Streak is primarily spread by water splash; proper plant spacing and minimizing overhead irrigation can slow disease development. The pathogen can also be disseminated by workers and tools, especially when leaves are wet. Leaf streak fails to develop when temperatures are above 90° F. Isolate infected plant material from healthy daylilies. Fungicides may be applied to protect susceptible new foliage and effective materials include: thiophanate methyl (Cleary's 3336, FungoFlo), myclobutanil (Eagle), chlorothalonil (Daconil, Echo 90DF), and azoxystrobin (Heritage).
Daylily Rust was first found in Georgia and Florida in 2000 and has since spread to 30 other states, including Massachusetts . The pathogen is native to Asia and is thought to have entered the United States on infected plant material from Central America . P. hemerocallidis first appears on the leaves as small, water soaked spots which expand and become raised to form pustules on both upper and lower leaf surfaces. Yellow-orange to orange-red spores are released from these pustules and can be carried by wind, water, workers, and tools. Although different cultivars react differently, most often infected leaves yellow, turn necrotic, and dry up. It is not known whether infection of tubers occurs. P. hemerocallidis requires two distinct hosts to complete its life cycle (heteroecious rust). The alternate host is the perennial Patrinia ; six species of this genus are grown and sold as ornamentals. However, on Daylily P. hemerocallidis produces polycyclic or repeating stage spores (urediospores) and does not require the alternate host for disease development. Once a Daylily plant produces spores the disease can spread rapidly to other Daylily plants. 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.
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.
Suspect Daylilies should be confirmed by a Diagnostic Lab. Contact M. Bess Dicklow at the UMass Extension Plant Diagnostic Lab at (413)545-3209, email@example.com . Sanitation is very important in managing this disease. Remove and destroy all infected plants. Purchase disease-free plants from reputable growers and propagate only from clean plant material. Minimize periods of leaf wetness by avoiding overhead watering and proper plant spacing. Protect uninfected plants with azoxystrobin (Heritage), propiconazole (Banner Maxx), myclobutanil (Eagle), chlorothalonil (Daconil), thiophanate-methyl (Cleary's 3336), triadimefon (Strike), or triflumizole (Terraguard). Check labels for broad crop clearance before applying fungicides.
More information and photos of daylily rust are available from the following websites:
- 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.
- Prepared by M. Bess Dicklow, UMass Plant Extension Diagnostic Lab, University of Massachusetts , Amherst , MA 01003 -9285.