COLUMBUS, Ohio - An ornamental plant disease, first diagnosed in Ohio last month, can pose a serious threat to daylilies.
Daylily rust, caused by a rust fungus of the Puccinia species, has been reported in Franklin and Cuyahoga counties. First reported in the southeastern United States last year, it also exists in Kentucky, Indiana and other midwestern states, and poses potential problems for nursery, greenhouse and garden growers.
"Daylily rust is a pretty serious disease," said Steve Nameth, an Ohio State University plant pathologist. "In Florida, if the disease is found in a greenhouse, that greenhouse is immediately quarantined. The ODA (Ohio Department of Agriculture) hasn't made any quarantine decisions as of yet, but we are following the situation closely to see what will happen."
The disease germinates on daylily leaves, producing lesions that cause leaf dieback. Since photosynthesis, the process of how the plant obtains food, is conducted through the leaves, limited number of leaves on the plant reduces its chances of surviving through winter. The disease spreads easily from plant to plant via spores carried by wind-driven rain and has a short incubation period, infecting leaves two to three days after inoculation.
In addition, it can not only germinate on its host plant, but can also produce spores via a secondary host -- a weed of the Patrinia species, which is also grown as a perennial. The presence of a secondary host increases the severity of infection. Six species of Patrinia are sold and grown in the United States as an ornamental.
Since little is known about the disease -- its biology, exactly how it reproduces, and what is needed for it to survive -- Nameth and OSU plant pathologist Mac Riedel will team up with Pat Henley, a daylily expert formerly with ODA, to conduct variety and fungicide studies beginning in September.
"We will study multiple varieties to see which ones show the most resistance to the disease. Pat has literally hundreds of varieties that we can use for the project," said Nameth. "We will also study which fungicides have the most impact on the disease. There are no fungicides on the market that are labeled specifically for rust on daylilies."
Nameth speculates that the wet spring aided in the development of the disease, which may have found its way to Ohio via transport of infected plant material. Growers concerned about the disease infecting their daylilies should cut the plants back to two to three inches above the ground, said Nameth.
The disease is characterized by a rusty spore mass that streaks along the leaf veins. Any leaves found with the disease should be removed from the plant and disposed of either through burning or placed in lawn bags and discarded.
"We are not recommending that people use the infected leaves as compost," said Nameth. "Also, prevent as much overhead watering as possible. Spores need moisture to germinate. If need be, water in the morning rather than at night so that the water has a chance to evaporate. If spores penetrate the leaves in damp conditions overnight, the plants will be infected by the next morning."
For more information on daylily rust, log on to
http://www.aphis.usda.gov/npb/daylily.html#Regulation or http://doacs.state.fl.us/~pi/enpp/pathology/daylily-rust.html.