The disease, day lily rust, was first identified in Georgia in August 2000, said Jean Woodward, an Extension Service plant pathologist with the University of Georgia College of Agricultural and Environmental Sciences. It has also been found in Florida, Alabama, South Carolina and California.
"Right now, the day lily rust is a concern for nurseries in the state," Woodward said. "The average gardener shouldn't be worried, but should be aware."
Apart from their beauty, day lilies have the reputation for being low-maintenance plants. The rust disease could compromise that reputation.
Stopping the Spread
"If we let the rust go and don't stop its spread, 10 or 20 years from now there may be a lot of day lily rust around," Woodward said. "There's a day lily in every garden and every roadside, and there's a chance this could spread.
"But because we were so quick to identify the rust, get the right people involved and get information out to major growers to watch the imported day lilies," she said, "we were able to get on top of this."
It has worked. Nurseries that had the rust, she said, aren't seeing it this year.
Woodward wants consumers and gardeners to be aware of the new disease, though. If you believe a day lily may be suspect, contact the county extension service.
Looks Like Streak, Acts Like Rust
|Daylily rust covers the upper and lower part of the leaf surface with orange spores.|
"If it (the day lily) has a sunk-in and water-soaked appearance," Woodward said, "(don't) be concerned. It's leaf streak."
If it's the new disease, though, within two weeks a fungus will produce powdery spores on the day lily. The bright orange spores will be on both the upper and lower leaf surfaces, she said.
The disease can spread fast, because the wind easily carries the spores. "Because it's rust, it's not going to kill the plant," she said. "The rust needs living tissue to survive."
The rust's survival depends greatly on the type of day lily. Georgia grows two types: dormant and nondormant.
The rust may not survive the winter on dormant varieties, Woodward says. But it will survive on nondormant types, as well as on older leaf tissue during milder winters.
"One year a day lily could experience the disease and the next year be totally free of it," she said.
Big Domestic Industry
Day lily rust is native to Asia. However, it's believed to have been introduced into at least one Georgia nursery from plants originating in Central America.
Day lilies are commonly shipped into the United States from Central and South America. Most of the day lilies grown in these countries, particularly in Central America, originate in the United States, not in Asia.
The actual origin of the disease, then, is a mystery. Woodward said it may have come to the United States from Europe. U.S. day lilies shipped to Central America were then shipped back to U.S. growers.
"If a grower has rust (in his day lilies), the grower should cut back the foliage, burn it and get into a fungicide spray program," she said.
Day lilies are the No. 1 perennial in the country, she said, and the Southeast produces most of the day lilies sold in the United States. Production of day lilies contributes greatly to Georgia's $400 million nursery industry.
Georgia is home to four of the top nursery growers in the country and the largest nursery east of the Mississippi River. "The industry is growing in Georgia at about 5 percent a year," Woodward said.
(Brad Haire is the former news editor with the University of Georgia College of Agricultural and Environmental Sciences.)