If those geraniums that looked so beautiful at the nursery last spring just didn't bloom well or ever look healthy in your yard, they may have had a virus or two.
"Viruses do not kill geranium plants, but some can severely reduce vegetative growth by affecting leaves and can reduce flower quality and marketability by deforming blooms and causing color breaks or streaks," says Agricultural Research Service plant pathologist Ramon L. Jordan. A plant virus expert, he leads the Floral and Nursery Plants Research Unit of the U.S. National Arboretum.
Jordan says confusion exists about the exact identity of some of the 15 or so different viruses attacking geraniums—a flower crop worth about $200 million a year to U.S. growers. Geraniums, genus Pelargonium, are one of the most rapidly expanding garden crops in the United States.
Now Jordan, working with ARS plant pathologist Gary R. Kinard, has developed new tests that use biotechnology to detect two of the newer viruses: pelargonium line pattern virus and pelargonium ringspot virus. The tests take about 24 hours.
Jordan says the new tests will help ensure that both exported and imported geranium plants—potted or in beds—are free of the two viruses.
Over the last 18 years, Jordan has been pursuing and identifying disease-causing viruses in ornamental plants, vegetables, and trees. What's tricky about the geranium viruses, he says, is the easy way they get around and the 1 to 3 weeks that it takes after infection for their symptoms to appear.
"An infected plant in the greenhouse can be the source of some viruses that can spread via water to the plant sitting next to it," he says. "Other viruses are spread by aphids, while tiny insects called thrips can transmit viruses or carry infested pollen from infected plants to healthy ones.
"Since geraniums are propagated mainly by taking cuttings from established plants, this is likely the most common method of virus spread."
Jordan is working on the other viruses that attack geraniums, as well as those that cause severe problems in such popular flowers as impatiens and gladiolus. -- By Hank Becker, ARS.
Ramon L. Jordan is in the USDA-ARS Floral and Nursery Plants Research Unit, U.S. National Arboretum, 10300 Baltimore Ave., Bldg. 010A, Beltsville, MD, 20705-2350; phone (301) 504-5646.