About Rose Virus
Rose Mosaic Virus
Have you ever had a rose with funny yellow lines on the leaves? Or leaves with random green/yellow blotches? If so, that rose probably had what is known as Rose Mosaic Virus (RMV). This is a serious disease that has affected a large percentage of the commercial rose stock in the United States. Along with those unsightly leaf markings, RMV can cause reduced vigor, a shorter life span, and decreased bloom production in roses. Other symptoms include: stunted growth, shorter flower stems, leaves that are distorted, puckered or smaller in size, poor transplant survival and decreased winter hardiness.
The easiest way to identify RMV is through the leaf markings it produces. There are several distinct patterns, but they all indicate the presence of RMV. The first, and most unique, is called “line banding” which produces leaves with yellow to whitish lines in a zig-zag pattern. Often this appears on the center of the leaf and resembles an Oak Leaf. Leaves can also have a great amount of yellow spots which remind you of mosaic tiles. This is called “mosaic” and is what gives the virus its name. “Watermarking” is another leaf pattern you might look for in a rose that has virus. It is characterized by faint, almost invisible swirls or squiggles in the green color of the leaf. Finally, “vein banding” looks like the reverse of iron deficiency; the veins are yellow and the leaf is green.
Rose Mosaic Virus is one of the more interesting rose ailments because it is highly variable and does not always present symptoms. Sometimes the virus causes serious damage; other times symptoms are mild and can be easily overlooked. Symptoms are more pronounced in spring and fall; the drier, hotter conditions of summer inhibit the virus. As a result, the virus may seem to “disappear,” with growth appearing normal in the summer. It is also not unusual for a plant to be several years old before showing any signs of RMV.
You may have noticed that Heirloom Roses produces only own-root, virus-free roses. How do we ensure our roses are virus-free? When most people think of a virus, they envision the common cold, something that transfers easily from one person to another. Thankfully, RMV is not contagious in the environment; adjacent rose bushes cannot “catch” it from a nearby plant that is infected. The virus 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.
Historically, RMV was virtually unknown prior to 1920, which was about the time the rose Dr. Huey began to be used industry-wide in the U.S. as a commercial rootstock. Some have also speculated the virus was introduced by grafting some wood from an apple tree onto a rose. While this bud would not take, it would eventually infect the rose with the virus. Regardless of its origin, no rose is immune to this systemic virus. Once an infected portion is grafted with a healthy cutting or rootstock, the virus will spread throughout the plant via the phloem (food-conducting) system.
Since Heirloom Roses produces only own-root roses, from rooted cuttings instead of by grafting, this greatly reduces the likelihood of our roses having virus. That is only half the story, however. We have to ensure that our stock plants used for cuttings are virus-free as well. At one point in time, it was estimated that up to 90% of the commercial roses in the U.S. were infected with virus. However, rose virus is not as big a problem in roses originating and grown in Europe (the majority of rootstock in Europe is grown from seeds which are virus free). For this reason, nearly every variety of rose sold by Heirloom Roses has been imported from Europe to ensure virus-free stock for our customers. For certain varieties that originated in the U.S., we have used a process called ‘virus-indexing’ to ensure virus-free stock.
Heirloom Roses is committed to ensuring our roses are virus-free. On the extremely rare occasion that one of our plants exhibits virus, that plant is removed and destroyed immediately, along with all of its retail cuttings. While others in the industry may not exhibit the same concern, we never market a variety that is known to have virus. That is our guarantee.
There are many other foliar diseases that can create symptoms similar to RMV. Make sure that you do not confuse RMV with the natural diseases that roses can attract like black spot, powdery mildew, rust and downy mildew. Certain mineral deficiencies in the rose may also resemble RMV. However, should you suspect one of your grafted roses has virus, the only remedy you have is to replace it – preferably with an own-root rose!