If you aim to strike fear into a rose breeder’s heart, all you need are three little words—“rose rosette disease.”
Rose rosette disease is an insidious rose killer. Spread by microscopic eriophyid mites, the virus affects only roses. There is no cure and it is almost invariably fatal. To make matters worse, no rose species or variety is immune. Even the ‘Knock Out’ rose, advertised as pest and disease resistant, is susceptible.
In many years of growing roses, I have dealt—mostly successfully—with black spot, powdery mildew, aphids, rose chafers and Japanese beetles. I have never encountered rose rosette disease until this year. Now it appears that at least three of my rose bushes are afflicted. Unfortunately they will have to be destroyed.
You will never see the mites, but the symptoms of rose rosette disease are fairly easy to spot. Rose bushes will develop atypical new growth, sprouting “witches brooms”—bunches of thicker, pricklier stems with slender red leaves that never turn green. These stem and leaf clusters look completely different than normal new growth on the shrubs. When flower buds appear, they are also deformed and rosette-like. The disease is systemic, so even if you prune off the affected parts, chances are the entire plant is ailing.
Like other notorious viruses, rose rosette disease is contagious. The mites that carry it cannot fly, but can be carried by the wind from plant to plant. This is a special threat to dedicated rose beds where shrubs are close together.
The main host plant for rose rosette disease is the multiflora rose, which was imported from Japan for use as a hardy rose rootstock in 1866. “Hardy” quickly morphed into “unstoppable” as the multiflora escaped domestic cultivation and began invading woodland edges, sunny roadsides, vacant urban lots and even untended corners of suburban backyards. It is very easy to recognize, especially in May, when the small, fragrant white flowers appear. Multifloras are thicket-forming shrubs with slender, flexible canes. The flower clusters are made up of five-petaled single blooms with centers containing bright golden stamens.
Pollinators love the fragrant flowers and birds gorge themselves on the small red hips that develop in summer. By doing what birds do best—eating and excreting—our avian friends help to spread multifloras over a wide area. When the plants are untended and untamed, the thickets grow to immense size, outcompeting less aggressive native species. Though lovely to look at, multifloras are a threat to local ecosystems. Their propensity for hosting rose rosette disease makes them dangerous to rose gardens as well. If you love roses, don’t let Rosa multiflora take root in your yard and give a heads up to your neighbors as well.
If you spot rose rosette disease on one of your roses, steel yourself for the inevitable. You are going to have to take it out—roots and all. If you don’t, the virus may spread to uninfected plants. The best way to remove the rose is to put a sturdy plastic bag over the top growth at the start of the process to keep mites from traveling. Dig out the whole thing, getting all the roots. Throw the bag in the trash, rather than composting the remains. Afterwards, be extra safe by disinfecting the garden tools that you used, washing your gloves and even washing the clothes you were wearing. Don’t go near other roses before taking those steps.
Even the most careful removal process may leave a few virus-infected roots in the ground, so avoid planting new roses in the same spot. Try another perennial or shrub that likes the same conditions—lilies, flowering weigela or peonies will all do the job.
To discourage mites, prune back roses hard at the end of the growing season, as the minute creatures tend to secrete themselves in the old flower buds. Don’t plant rose bushes too close together and make sure all roses have good air circulation within and around the shrubs.
I love roses and I will not let rose rosette disease stop me from growing them. My heart is heavy at the thought of taking out two of my oldest and most productive bushes, not to mention a lovely newcomer, but if doing so will save the many other treasured plants, it is a price I am willing to pay.
And one more thing—if you are like me and tend to blame yourself for plant failures, take a deep breath or a long walk. The mite, though microscopic, is bigger than you are. Enjoy your remaining roses, stay away from multifloras and know that the “bad guy” in rose rosette disease is the virus, not the gardener.