Texas Cooperative Extension,
Texas A&M University, College Station, Texas

April 2004


Daylily Rust - An Avoidable Nuisance


The All-American Daylily Selection Council

Daylily rust, photographed by Dr. Larry Barnes
Example of daylily rust photographed by Dr. Larry Barnes,
Dept. Plant Pathology, Texas A&M

Since its discovery in 2000, daylily rust (Puccinia hemerocallidis) has been found in daylilies in over half of the United States. The infection does not kill daylilies and, according to the All-American Daylily Selection Council (AADSC), can be avoided by proper selection and horticultural practices. In a worst case scenario, daylily rust can be controlled by treatment of the susceptible varieties. The University of Georgia, led by Dr. Jean Woodward, has done most of the key work on daylily rust so far. She has identified chemicals that are appropriate for control and performed greenhouse testing of varieties to determine their susceptibility or resistance to the new pest. The AADSC, in the course of its normal multi-year field testing of daylily varieties, has made some findings that should complement the work of the University of Georgia. As can be expected, the results of long term, multi-year field testing and observations are not always 100% correlated with the results of greenhouse testing. Field conditions provide additional variables that can affect how severely a plant responds to the presence of rust.

Daylilies infected by Puccinia hemerocallidis show unsightly rust spots and yellowing, mainly on older foliage, similar to rust symptoms on roses, geraniums and other garden plants. The rust is confined to the foliage and bloomstalks (scapes) and has not been shown to enter the crown or roots. Puccinia spores spread quickly by wind, on clothing and infected plants, but do not infect other plant species. Roses have their own specific rust species, as do most other ornamental plants. Just as with roses, symptoms of daylily rust vary greatly depending on growing conditions and the susceptibility of each variety. Among the 48,000-plus daylily cultivars are varieties that are unusable in some gardens and those that are virtually symptom-free.

The worst rust symptoms will appear on daylilies grown in conditions of high humidity, poor air circulation and nighttime overhead watering. Daylily rust spores require 100% humidity and temperatures between 40 and 90 degrees F. for five to six hours to germinate. If germination does not occur within two to three days, the spore dies. If germination occurs, infection can lie dormant within green tissue until optimal conditions arise. It appears that spores do not survive outdoors in winters colder than USDA Zone 6, making daylily rust more of a problem in warmer areas.

In 2001 rust resistance was added as one of the key test criteria for performance evaluations in daylilies. In selecting for "bulletproof" performance, the AADSC has eliminated many of the highly susceptible varieties from its program and focused on identifying and promoting the most rust-resistant daylily varieties.

More than 700 varieties have been or are being put through rust trials b the AADSC and University of Georgia, as well as Cornell University and the USDA. Here are the results on some of the most commonly available varieties:

Susceptible

  • Pardon Me
  • Ming Toy
  • Russian Rhapsody
  • Always Afternoon
  • Mary Todd
  • Pandora's Box
  • Strawberry Candy
Moderately Susceptible (USDA):

  • Happy Returns
  • Prelude to Love
  • Gertrude Condon
  • Stella D'Oro
  • Joan Senior
  • Butterflake
  • Wilson's Yellow
  • Star Struck
  • Crystal Tide

Least Susceptible Varieties

  • Little Business
  • Mini Pearl
  • Butterscotch Ruffles
  • Mac the Knife (USAD)
  • Yangtze (USDA)
  • Holy Spirit (USDA)

Among the AADSC's "All-American Daylilies," Black-Eyed Stella, Lullaby Baby, Bitsy, Frankly Scarlet and Plum Perfect have been reported as rust resistant; Judith as moderately resistant; Star Struck as moderately susceptible, and Leebea Orange Crush as suceptible.


Note: This material appeared in the web periodical Horticulture Update, Drs. William C. Welch and Douglas F. Welsh, Editors, Department of Extension Horticulture, Texas A&M University, College Station, Texas

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