In the spring, you might notice yellow spots that look like tiles on your rose bush leaves. Or yellow lines in a pattern that resembles an oak leaf. Maybe you’re seeing light squiggly lines or yellowing along the leaf veins. It might be on just one section of your shrub. Is it caused by an insect? Or a fungus?
Probably not. Most likely, it’s Rose Mosaic Virus, an incurable disease. Roses get lots of diseases, and many are curable. This is not one of them. But don’t panic! This disease is rare, and a shrub can live with it for a long time if properly cared for otherwise.
What is Rose Mosaic Virus?
Sometimes called Rose Mosaic Disease, RMV can be a combination of viruses – Arabis Mosaic Virus (ArMV), Prunus Necrotic Ringspot Virus (PNRSV), or Apple Mosaic Virus (ApMV). If there is more than one virus infecting your plant, it’s called a complex.
The only way to know for sure is to send a sample to your county extension service. But whichever virus or complex is infecting your rose bush, the symptoms all look the same.
What Causes It?
Unlike fungal and bacterial diseases, which are on the plant and are most often spread by wind and water, viruses are in the plant – they need to physically enter the plant to infect it. For some plants, this is caused by insects.
RMV is spread during production, when cuttings are grafted onto infected rootstock. If the rootstock or the cutting has the disease, the rest of the plant will become infected by drawing the virus through its vascular system as the two plant parts fuse together.
Rose Mosaic Virus doesn’t spread to other plants by infected pruning tools, insects, water or air movement, or from plants touching each other. Occasionally the roots of two rose bushes can fuse together, and an infected plant can pass the disease to a healthy plant, but these occurrences are rare.
Some rosarians think that RMV can be spread by pollen and aphids, but that has not been proven.
Symptoms first show up in spring and continue through the growing season. In hot, dry summer weather, the symptoms may subside but will reappear in the cooler fall weather.
The virus causes less chlorophyll to be produced in parts of the leaves.
Symptoms vary depending on the Rosa cultivar, environmental conditions like weather, and the virus itself. Symptoms include puckering of the leaves, lighter green or yellow lines, spots and blotches, yellowing along the veins, and mottling. Discoloration can be red or orange too, and flower color might “break.”
Mosaic tiling – almost rectangular yellow blotches that look like tiles
Line banding – leaves with yellow lines that look like an oak leaf
Watermarking – faint squiggles, blotches, and lines
Vein banding – green leaves with yellow veins
Once infected, a rose bush will have this disease for the rest of its life.
It can cause stunted growth, decreased flowering, early leaf drop, decreased winter hardiness, and can shorten the life of the plant.
Infected plants can be dug up and destroyed, but because the disease will not spread to other plants in your garden, removal is completely up to you. If you are unhappy with the look and performance of your infected shrub, remove it. Then buy a new, healthy plant from a reputable nursery that carries plants from breeders who certify that their products are virus-free.
Prevention and Control
Because this disease is caused during production, there isn’t anything a home gardener can do to prevent it. It’s bred into the plant when growers don’t use virus-free plant material.
Infection occurs during propagation by budding or grafting.
Grafting and budding are propagation methods that involve inserting a stem or bud from one plant into the root system of another plant. The plant parts fuse together, one plant growing on the other. This is done because the rootstock of one plant is hardier than the rootstock of the other, but the blooms are not as desirable. Grafting and budding are used to propagate lots of different plants, not just roses.
Breeders and commercial growers are working hard to prevent this disease. They don’t want sick plants any more than you do! Many get their root stock from the National Clean Plant Network.
The National Clean Plant Network – begun in 2006 – is an effort by the US Department of Agriculture to provide healthy plant material for propagation to growers and breeders. Plant material can include rootstock, stem cuttings, and seeds. Roses have been part of the NCPN since 2015.
Foundation Plant Services at the University of California Davis has a clean rose block with 500 cultivars and growing; there are also clean blocks at Texas A&M and the University of Wisconsin-River Falls. Testing is extensive – 3 tests are administered over 2 years before stock can be certified as clean.
What Can a Gardener Do?
First, buy plants from a reputable nursery that carries certified virus-free roses. A few growers to look for: Heirloom Roses, Jackson & Perkins, and David Austin Roses.
If you do have an infected shrub, you can choose to dig it up and destroy it. But because RMV is unlikely to spread to other roses in your garden, you can leave it as long as you are happy with its appearance.
If you keep a sick rose, care for it. Keep it properly watered and fertilized, add mulch in the winter, and deal with other diseases and pests right away.