News isn’t good at all for roses infected by new, strange virus

Published 12:00 am Sunday, September 20, 2015

Earlier in the week I was working on a short presentation I’m making soon on dealing with rose pests, the audience being our small rose organization that meets monthly in Clinton.

Until recently, talks on rose disorders were 90 percent blackspot of rose disease and 10 percent every other fungus or insect that might show up.

But here of late, the sure enough rose folks have been interested in the virus-caused problem of rose rosette.

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I know that common name for a plant disease almost sounds redundant: rose and rosette.

The term rosette was used well before roses developed this problem.

Probably the plant longest known to have a rosette disease in this part of the country is blackberry.

For many years we’ve dealt with blackberry rosette, so called because the distorted blackberry bloom of infected plants has extra petals and reminded somebody of a rose bloom.

For the same reason, the disease is also called blackberry double blossom. And because new stems and leaves of infected plants tend to grow bushy and twisted and elongated, the term witches broom is also used for both infected roses and infected blackberries.

However, it is a different virus species that cause the problem in the two plants. Roses and blackberries cannot infect one another with rosette.

It’s debatable whether rose rosette has made it as far south as Interstate 20 yet. It has been positively identified a few miles north and there are reports of the disease in the central Mississippi area. If not here, it is merely a matter of time and it certainly will be since it has spread southward for many years.

The known information about rose rosette is all bad. There is no cure. Remember, this one is a virus, not a fungus or bacteria. So there is no fungicide or antibiotic to spray.

And even worse, it appears just about all roses, including the popular Knockout varieties, are susceptible.

So far, the recommendation for dealing with infected plants is to pull them up roots and all. Bag infected plants tightly in plastic and send them to the landfill.

Researchers are pretty sure the rosette virus is spread by a tiny mite species within the Eriophyid mite group. The microscopic bugs are less than 1/200th inch long, so don’t even bother looking for one.

There has been thought about the possibility of the virus being transferred by natural root grafting, the underground joining of roots from two plants. So far, that has not been proven. However, since rose plants, like most ornamental perennials, are propagated by cloning, any infected plant that is rooted would pass on the virus.

Ditto for plants propagated by grafting, and either the grafted cutting or the rootstock would guarantee the virus in the offspring if either were infected.

Since I know more about blackspot, I’ll likely give it more time today. I did take pictures of some unusual insect galls on roses in Nova Scotia this summer. But those pictures were on the iPad that stayed on the plane in Atlanta.

Terry Rector writes for the Warren County Soil and Water Conservation District. You may reach him at 601-636-7979 ext. 3.