Prized by gardeners, enthusiast clubs, and commercial growers, dahlias are a perennial flower favorite. Northwest-grown dahlias are bred in myriad colors and forms and sold for export nationally and beyond.
Washington State University scientists, led by plant virologist Hanu Pappu, partnered with the American Dahlia Society, a nonprofit association of more than 2,000 enthusiasts and growers, to study dahlia viruses and encourage better routine practices to stop viruses’ spread.
Dahlias face major challenges from several different, damaging viruses prevalent across the United States. Severe infection stunts growth and can prevent the valuable blooms from developing at all.
Pappu, a Dahlia virologist, has identified new dahlia viruses and developed rapid, sensitive viral detection methods. He directs the Clean Dahlia Center at WSU, supported financially by the Scheetz-Chuey Charitable Foundation.
Sold nationally and internationally, dahlias are a valuable crop for growers across the U.S. Above, blooms in a range of colors and forms at the Swan Island Dahlias farm in Canby, Ore.
Dahlias are propagated from tubers and cuttings. If a mother plant is infected, its child plants will be infected, too, with viruses accumulating in dahlia crops over time.
“By using tubers and cuttings, we’re unintentionally spreading viruses to the next generation,” said Pappu, WSU’s Chuey Endowed Chair in the Department of Plant Pathology.
“Some of the viruses that infect dahlias are both contagious and highly stable—similar to COVID-19,” meaning they don’t break down easily outside their hosts, Pappu said. “A simple cut by an uncleaned knife used on an infected plant is enough to transmit these viruses to other plants.”
One simple, effective way to stop the spread is to disinfect cultivating tools such as knives and scissors, using a 1:10 diluted solution of household bleach, or Virkon S, each time between working with different plants.
WSU virologist Hanu Pappu, taking part in a dahlia society annual meeting and show in 2021.
To encourage growers to adopt clean propagation methods, Pappu partnered with Ron Miner, past president and current executive board member of the American Dahlia Society. “It looked like a simple enough practice that could go a long way in reducing virus spread,” Miner said.
An Ohio resident and engineer by training, Miner and his wife Barbara have grown dahlias for decades. Consulting with Pappu, Miner experimented with disinfectants in his own dahlia garden, then shipped plants to WSU for testing to examine the effect of garden practices on viral presence.
“Growers pay attention to fellow growers,” said Miner, who asked fellow dahlia enthusiasts and longtime growers Nick Weber of Maryland, Jerry Moreno of Ohio, Linda Taylor of Oregon, and Brad Freeman of Redmond, Washington, current Dahlia Society president, to try out the techniques.
They shared their experiences with fellow growers at dahlia clubs and national meetings, in person and via Zoom, encouraging all enthusiasts to adopt better routine practices. Pappu and Miner also teamed up to present at national American Dahlia Society meetings and share knowledge through its quarterly bulletin, an important source of information for the U.S., Canadian, and international growers.
“Professor Pappu and his team have provided us with practical counsel on how to reduce the incidence of the virus in our gardens,” Miner said. “We’ve generated a lot of field data that supports the WSU guidance. Our members recognize the benefits of the work and are beginning to use it to improve the appearance and the performance of their gardens.”
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