Management of rust on field and container-grown daylily in Georgia

Summary

Daylily is a popular, herbaceous perennial and is favored by landscapers and producers in the U.S. as a low maintenance plant with few insect or disease problems. In 2000, daylily rust was first detected in the Southeast U.S. and quickly spread throughout much of the country due to widespread movement of the pathogen on infected stock and subsequent establishment in the landscape. Daylily rust can negatively affect the production, distribution, sales, and cultivation of daylilies because infected plants often are not marketable. Improved disease management options will continue to reduce the impact of daylily rust on Georgia producers.

Situation

Differences between isolates of Puccinia hemerocallidis in the ability to cause lesions on some cultivars of daylily suggest that genetic subdivisions termed “races” of P. hemerocallidis are present in the U.S. A race of the fungus carrying a non-virulent (or avirulent) gene would not be able to infect a daylily host with a corresponding gene for resistance but would cause disease on a daylily cultivar lacking this gene. Races are commonly reported in the rust pathogens that attack field crops such as wheat and barley – as new races emerge, corresponding resistance genes need to be moved into in the host genome by breeders to minimize disease losses. If new races of the fungus exist that can overcome resistance in the host more effective disease control options are necessary. Fungicide dips on bare-root plants or drenches to daylilies in greenhouses and nurseries would further reduce the potential risk of moving daylily rust on infected plants and reduce the impact of this disease on growers.

Response

Sixteen isolates of Puccinia hemerocallidis collected over a four year period were tested for their infection type on twenty-one daylily cultivars obtained from a commercial grower. Differences in disease responses between isolates confirmed the presence of different pathotypes of the fungus. Soil drenches and foliar sprays were evaluated in field experiments in Griffin, GA in 2010 and 2011. Dipping bare-root daylily plants for 5 min in azoxystrobin, tebuconazole, or thiophanate-methyl significantly reduced lesion development compared to non-treated control plants. Drenches with azoxystrobin, fluoxastrobin, or tebuconazole, each at three rates (0.06, 0.12, and 0.24 g a.i/container), significantly reduced development of rust lesions on container-grown daylilies for up to 9 weeks after treatment. One early season drench of azoxystrobin at 0.12 g a.i./plant provided season-long reduction in disease incidence and disease progress that was comparable to foliar sprays with azoxystrobin or chlorothalonil applied at 14-day intervals. Dip or drench applications of fungicides would allow growers to diversify rust management options and could reduce the number of foliar fungicide applications.

Impact

The presence of races of the daylily rust fungus suggests that cultivars of daylily previously thought to be immune to the pathogen could be at risk of infection. The use of single drench applications of fungicide for season-long disease control would reduce the labor costs associated with multiple foliar applications of fungicide.

State Issue

Agricultural Profitability and Sustainability

Details

• Year: 2012
• Geographic Scope: State
• County: Spalding
• Program Areas:
  • Agriculture & Natural Resources