The most popular rose in Tennessee is in big trouble after an attack by an insect virus. Experts are working on a cure, but in the meantime, they say to watch your plants carefully.

Scientists at the University of Tennessee Agriculture Extension program say about one-third to half of all knockout roses in Middle Tennessee are suffering from the disease.

The knockout can bloom from early spring until Thanksgiving and doesn't get black spot - the disease that ruins so many fancy roses.

The knockout lived up to its name from the day it was introduced to the state in the 1990s.

"If you're looking for a rose where you didn't have to apply fungicides or, really, any insecticides, this was the rose that the average person could grow," said Alan Widham, Ph.D., plant pathologist at UT Extension.

But then, all of a sudden, this insect disease first showed up about three years ago, causing small bunches on the top of the stems called rosettes.

"One of the things you look for is excessive thorns on the cane," Widham said.

You can prune back, but generally the bush will die, and you can't replant until the next season. That way, the microscopic bugs that are killing the rose have time enough to die.

"They're tiny little mites that are probably spread by animals, possibly by the wind. They're so tiny. They get inside the flowers and the leaves," said Frank Hale, Ph.D., entomologist at UT Extension.

Alternative plants have been suggested, but none measures up to the knockout rose.

Widham said when you see a rosette, cut it back immediately as far as your can and hope to keep the rose alive at least through the season.

For now, there is no cure for the disease.

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