Identifying And Treating Rose Mosaic Disease


By: Stan V. Griep, American Rose Society Consulting Master Rosarian, Rocky Mountain District

By Stan V. Griep
American Rose Society Consulting Master Rosarian – Rocky Mountain District

Rose mosaic virus can wreak havoc on the leaves of a rose bush. This mysterious disease typically attacks grafted roses but, in rare cases, can affect ungrafted roses. Keep reading to learn more about rose mosaic disease.

Identifying Rose Mosaic Virus

Rose mosaic, also known as prunus necrotic ringspot virus or apple mosaic virus, is a virus and not a fungal attack. It shows itself as mosaic patterns or jagged edged markings upon the leaves of yellow and green. The mosaic pattern will be most obvious in spring and may fade in the summer.

It may also affect the rose flowers, creating distorted or stunted blooms, but often does not affect the flowers.

Treating Rose Mosaic Disease

Some rose gardeners will dig out the bush and its soil, burning the bush and discarding the soil. Others will simply ignore the virus if it has no effect upon the bloom production of the rose bush.

I have not had this virus show up in my rose beds to this point. However, if I did, I would recommend destroying the infected rose bush rather than take a chance upon it spreading throughout the rose beds. My reasoning is that there is some discussion about the virus being spread through the pollen, thus having infected rose bushes in my rose beds increases the risk of further infection to an unacceptable level.

While it is thought that rose mosaic may spread by pollen, we know for a fact that it does spread through grafting. Oftentimes, rootstock rose bushes will not show signs of being infected but will still carry the virus. The new scion stock will then be infected.

Unfortunately, if your plants have the rose mosaic virus, you should destroy and discard the rose plant. Rose mosaic is, by its nature, a virus that is just too tough to conquer currently.

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RMV does not kill plants, affect the vigor of plants, or reduce the size or quantity of blooms. People say it sometimes does this, but I suspect something else was the cause, because I have dozens of roses with RMV, most of them for at least 20 years, and it hasn't had this effect on them. I have some duplicates, and there's no difference whatsoever in the quality of the virused and non-virused plants.

RMV does not spread to other roses. Scientists have conducted experiments to try to spread RMV from one rose to another, and they have always failed. RMV is only spread by cuttings. If you take a cutting from an affected rose, the plant that grows from that cutting will have RMV.

RMV is not confined to modern roses or to roses on this continent. Roses from Europe can also have RMV and there's an impressive list of OGR's that don't exist in non-virused form. Rose de Rescht is probably the most frequently cited example. No one has a non-virused Rose de Rescht.

So, unless you insist on perfect foliage, there's no reason to dig up and discard a rose with RMV.

I think they were thinking of the watermark type of pattern that is characteristic of PNRV. But I think it does resemble one of the types.

Now that I've praised 'Caramella 86' & drawn attention to the fact that it's available from only 1 source, I feel I've an obligation to mention the unfortunate fact that the own-root plant in my present garden is virused. I grew this rose for 3 or 4 years before unmistakable RMV symptoms appeared for the first time in 2006. Since then, symptoms have not returned, but I now know for certain that the plant is infected & that it's only a matter of time before the evidence will resurface. Thus far, the plant's vigor appears normal & bloom production remains high. I grew Caramella for a number of years in a previous garden & do not recall ever encountering signs of RMV -- which, of course, does not mean that the plant was definitely not virused. For what it's worth, I'm almost certain that my first plant was grafted.

Comments from the experts here?


I am relieved that the virus doesn't spread by basic garden methods - using the same tools on roses, etc.

Is your Carmella showing any signs of virus?

Last year, I read about lily virus and was inspired to move my tiger lilies to a different garden to be away from my regular lilies. (These are the actual tiger lilies with the little bulbs along the stem not the orange ditch lilies that people call tiger lilies). Tiger lilies can carry the virus and not show symptoms. Lots of "experts" strongly recommended that they be away from oriental lilies. My tiger lily was a "rescue" from an abandoned garden by a fire damaged building barely surviving under piles of lumber and debris. All my other lilies look fine (albeit crowded because they multiplied over the winter). Very few people garden around here. I haven't seen any other lilies in town. I don't think that lily virus is a concern in my garden unless I buy new lilies from a disreputable vendor. It seems that lily virus can be spread by pollinators or garden tools. I have a couple tiger lilies popping up again in the original garden bed near the coral carefree celebration rose. I think they will look nice together, so I am leaving them there this year!

From what I have read, hosta virus seems to be the most easily spread. It also seems to seriously weaken the plant. Two women were talking about hosta virus at the local Lowe's and pointing out plants to the manager - buyer beware, I guess. I didn't get a look at the plants or a chance to talk to the ladies, was in a hurry that day. I only have a few hostas including a huge green variety (perhaps sum and substance) plotting world domination. Have to admire any plant that can grow in deep shade under black walnut trees with little care, but roses are much sexier.

I have only seen pictures of rmv, not the real thing. Most pictures show the yellowing of the leaves, but one site showed "broomstick" growth where the rose foilage was very deformed. Do you encounter mostly the discolored leaves?


Rose Mosaic - How To Treat Rose Mosaic Virus - garden

Q: Last year I purchased a climbing ‘Constance Spry’ rose which really grew quite large, over 15 feet, in one season. This year I have noticed that many of the leaves have yellow speckling and the very, very few flowers that have appeared so far are deformed.

A: I bear bad news. Your rose has mosaic virus. Like human viruses, there is no cure for plant diseases caused by a virus. A plant virus is spread by insects your problem could even have come with the rose when you purchased it.

The cure for rose mosaic virus is severe: pull up and destroy the plant. Nothing you can do will bring it back to health. The longer you keep it in your garden, the longer insects have to infect other roses in the neighborhood.

Personally, I’d call the vendor and ask for a replacement. One year is mighty quick for a clean rose to become infected with a virus, especially if you have no virus-infected roses in your garden.


Heirloom Roses Ensures Virus-free Roses

Heirloom Roses produces only own-root, virus-free roses. How do we do that? When most people think of a virus, they envision the common cold, something that transfers easily from one person to another.

RMV is not contagious in the environment adjacent rose bushes cannot “catch” RMV from a nearby plant that is infected.

RMV spreads only through grafting, where the cutting of a desired rose variety has been grafted onto the rootstock of another variety. Grafting has been the traditional method of rose production in the United States. Heirloom Roses pioneered the practice of producing own-root roses for commercial resale to ensure virus-free roses.


How do you recognize rose rosette disease in the landscape?

Early detection of the disease is crucial to keep other nearby roses healthy. However, early detection can be difficult because symptoms such as witch’s brooms and misshapen leaves mimic damage typically caused by herbicides. Roses should be inspected for symptoms in the spring when new growth starts to appear. The appearance of these symptoms will increase as the growing seasons progresses. Symptoms may vary by rose species or cultivar. Some common symptoms of rose rosette disease are listed below.

Distorted flower petals
Millie Davenport, ©2013 HGIC, Clemson Extension

  • Shoots and foliage have an abnormal red color
  • Stems appear thick and succulent
  • Rapidly elongating shoots
  • Shoots with shortened internodes
  • Stems with an overabundance of pliable thorns
  • New growth may have many branches that create a witch’s broom (similar to glyphosate injury)
  • Distorted or dwarfed leaves (similar to 2.4-D injury)
  • Deformed buds and flowers
  • Abnormal flower color
  • Lack of winter hardiness
  • Spiral cane growth

Mildew

Powdery mildew (Podosphaera pannosa) first appears on young leaves as crinkling on the edges, developing into spore-bearing fungal filaments that look like a thin, powdery film on every part of the plant, including buds. Sprinkling the leaves with overhead irrigation can disturb the spore's cycle, but the leaves need to dry before evening. Downy mildew (Peronospora sparsa) affects roses in moist, humid environments, such as coastal California. Symptoms are interveinal, angular purple, red and brown spots on the leaves, which eventually turn yellow and fall.

Roses on the West Coast are often impaired by rust (Phragmidium mucronatum), a fungus that grows in cool, moist weather and displays as raised red-orange spots on the undersides of leaves and yellow spots on the top. Rust spots or streaks can also appear on the canes. Plants can tolerate some damage but if left untended, the rust spots will form large groupings, turning black in the autumn. Potentially the whole plant could be defoliated.



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