For hobbyists like Colette Theriault, a photographer who lives in Ontario, orchids are an addiction. Theriault bought her first Phalaenopsis in 1999 and nurtured it for three years before it bloomed its first pink flowers. The success led to more, until she had 25 orchids crowding her windowsills. In March she discovered yellow spots on the leaves of her collection—a telltale sign of a virus, like those plaguing the orchid industry.
Theriault is now fighting a losing battle to save the first orchid she ever bought. "It's psychological for me," she says. "I was mad at myself for buying more plants."

Not long ago, only a rarified elite kept orchids in their homes. Collected from the tropics, orchids transported to other climates lacked the conditions needed to flourish and were nearly impossible to breed. But in recent decades growers have learned how to clone thousands of identical plants, and an industry has grown around the flowers. As growers have bred increasingly baroque varieties, sales have exploded, making orchids the second most sold houseplant in the U.S. (after poinsettia). Go to any Home Depot and brazen sprays of purple orchids are on display along with aisles of drywall and doorknobs. Even corner bodegas in big cities tend to carry a droopy Phalaenopsis or two for sale as house gifts.

View a slideshow of orchids

The popularity of orchids culminates in spring displays that pull in huge crowds. Last month, their strange and colorful petals drew 117,000 gawkers to the Bronx for a radiant exhibition at The New York Botanical Garden. Another legion of aficionados will descend on Oklahoma City for the American Orchid Society meeting this month.

As the orchid business has leapt from $47 million in 1996 to $123 million a year, a batch of viruses has bedeviled orchid greenhouses. "It's ruining the business," says Joseph Silva, co-owner of Silva Orchids in Neptune, N.J.

There are 30 known orchid viruses, but when growers say a plant has "a virus" they usually mean one of the two most prevalent: Cymbidium mosaic virus (CMV) or Odontoglossum ringspot virus (ORSV). Neither causes any obvious signs, but once orchids contract them, the plants begin to limp along—with fewer, shorter-lasting flowers. Then brown spots begin to appear on the leaves, the petals mottle and wilt, and the plant ultimately succumbs.

Tellingly, viruses do not naturally spread among wild orchids, which multiply by producing hundreds of thousands of feather-light seeds, none of which can carry viruses. So the only vector for spreading CMV and ORSV are the growers themselves. In some cases, careless producers have cloned infected plants and inadvertently sold armies of orchids bearing viruses. More commonly, workers spread the virus with their clippers. Unless heated or bleached between each trimming, the blades play the part of a dirty syringe.

"Orchid growers divided plants indiscriminately, gave them to friends, sold them. It didn't take long for one infected plant to infect thousands—never through the air, never through insects, but simply by human propagation," says Bill Zettler, a plant pathologist at University of Florida.

There are no current statistics on the prevalence of viruses. But studies during the last 20 years show a startling rate of both CMV and ORSV. Viruses infected 50 percent of the orchids tested in Singapore's botanical gardens in a 1994 study, 25 percent of those grown in Hawaii in 1993, and 65 percent of the cut orchids from Thailand, the world's largest exporter, in 2005.

Currently, at least two groups of orchid scientists, one in Hawaii and another in Singapore, have begun trying to solve the problem by genetically engineering breeds that resist CMV and ORSV. Sek Man Wong, a plant pathologist at the National University of Singapore, is using RNA interference to splice virus RNA into the plant's genetic blueprint. Theoretically the virus signatures should allow the plant to recognize and eliminate a potential infection. He hopes to have the genetically modified orchid ready for the market by 2015.

In the meantime, the percentage of infection among growers worldwide has likely dropped in the years since industry groups such as the American Orchid Society turned a spotlight on the issue. Ron McHatton, chief operating officer of the American Orchid Society, has been trying to quell a rash of gossip about viruses because, over the last few years, growers fingered Taiwan for continuing to spread the contagion. As the largest potted-orchid exporter, Taiwan delivers $21 million in Phalaenopsis orchids each year.  "People are saying the industry is riddled with virus. It's just not true," McHatton says.

Chin-An Chang, the former head of the plant pathology at the Taiwan Agricultural Research Institute, thinks it's unreasonable to ask for virus-free orchids because market prices are now so low. "A serious hobbyist who's concerned about viruses can go directly to the nursery for high quality. For the consumers buying it from the supermarket, some percentage of virus should be acceptable." That is hardly comfort for fans, who primp and beautify their orchids and end up infecting their entire collections.