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Award of Merit Article

Mosaic Virus

GARDEN BAD GUYS - ROSE MOSAIC VIRUS
by Nanette Londeree, Consulting Rosarian

If you notice some unusual markings on the leaves of your roses at different times of the year, that seem to have no adverse affect on the plant, you may have a plant infected with Rose Mosaic Virus (RMV). This disease is caused by Prunus Necrotic Ringspot Virus and is the most commonly found virus in roses. The symptoms generally appear in spring and appear as irregular coloration on the leaves - yellow zigzag patterns, splotching, or vein clearing. The disease can also produce distorted growth of leaves, flowers or growing tips. Plants infected with virus usually are slower to develop in spring, and produce fewer good quality blooms. Overall damage from the disease may be mostly cosmetic with little reduction of plant vigor. The signs may show up very intermittently and a rose may go for years without ever showing any sign that the disease is present. Then suddenly, a number of leaves may show the characteristic mosaic patterns. During the warm summer, typical symptoms can disappear only to come back as fall and cooler temperatures.

Mosaic Virus

RMV is not transmitted through vectors; it is primarily spread through propagation of plant parts – either through use of infected rootstock or buds for budded roses, or cuttings taken from diseased plants. You can’t infect a healthy rose by using cutting tools you have use on an infected plant. Recent research at the Foundation Plant Services at UC Davis has shown, however, that infection may be spread through the roots of an infected plant, though it is not known at this point if it is a result of grafting of roots between a healthy and diseased plant or transmission by nematodes.

There are no known treatments for the elimination of RMV for the home gardener. The primary approach should be the purchase of healthy plant material. For the past 40+ years, commercial rose growers have been working diligently to eliminate rose mosaic and other viruses in roses. They purchase rootstock that has been “virus indexed”, which means that the rootstock has been tested in a laboratory to confirm the absence of the virus in the plants tissue. If there is no plant material available that has been confirmed to be free of the virus, the desired plant stock can be heat treated in an attempt to eliminate the virus from the living plant. Roses are held at temperatures above 100 F for several months. The heat-treated plants are then used as source material for propagation.

When shopping for your roses, look on the package label or in the catalog for indication that the roses have been virus-indexed, or are virus-free (suppliers may use different terminology to convey the information). If you discover the disease in the spring after planting your rose, reputable suppliers will replace your plant. If you have a severely infected plant, you should dig it up and destroy it.


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Last Modified: 08/06/2013