Many gardeners steer clear of roses in an attempt to avoid the difficulties that may come with growing them. But in 2000, a rose came on the market that was truly low maintenance and disease resistant, it was what everyone was looking for in a rose and quickly grew to be the fan favorite…at least until now. In the last few years the Knock Out brand of roses have taken a tremendous hit; but the question is, will they stay down for the count?
What’s the problem?
Many Knock Out roses have been diagnosed with Rose Rosette disease. Rose Rosette is a viral disease that is spread by a tiny mite and is fatal to the rose that it has infected. The eriophyid Mite is simply a carrier of the virus and transmits the disease when it bites into the rose. It is a quarter of the size of a spider mite and while it can’t fly, it is so tiny that it floats on the wind from one rose to the next.
Oddly enough, this arch nemesis of the Knock Out Rose was once considered a natural biological control for wild roses. Back in the 1930’s, many conservation departments planted wild roses (Rosa multiflora) for soil erosion control; while these hardy roses seemed to solve many problems of the time, they quickly became invasive. Proving difficult to eliminate, Rose Rosette showed up in the 40’s and eradicated some but not all of the wild rose problems of the time. The virus then began to spread into our gardens and started to affect shrub roses and most recently, our Knock Out Roses.
Does this virus affect only Knock Out Roses?
No. Because of its low-maintenance, drought tolerance, and resistance to powdery mildew and black spot, Knock Out roses were highly marketed and planted widely. When a plant of one variety is planted in mass and close together it allows for easier spread of insects and diseases. Whether it is Knock Out, Drift Rose, Carpet Rose or any other shrub rose, the same problem can occur. Luckily Rose Rosette only affects roses and no other shrubs so you don’t have to worry about it taking over all the plants in your garden.
How can I tell if my rose is infected?
The appearance of this virus can be difficult to see in the spring but symptoms increase as the season progresses. Here are a few common symptoms to be aware of:
• Abnormal red color in the foliage and shoots
• Shoots that rise above the rest of the plant
• An abundance of soft thorns on stems
• Thicker stems
• Deformed and/or yellowed leaves
• New growth that has a mass of branches on the top, also known as ‘Witches Broom’
Will it kill my rose or can I treat it?
Rose Rosette is a fatal, systemic virus that infects the leaves all the way to the root system. Unfortunately, miticides and horticultural oils prove to be ineffective. Once a shrub rose is infected, the only option is to tear out the rose and dispose of it completely.
To do this, you need to dig out the root system and place the entire plant in a plastic bag to throw away taking careful measure to remove all debris left on the ground. Do not put the rose in the compost pile, be sure you dispose of it completely.
Can I plant another rose in the same spot I removed my diseased one?
Some professionals believe that as long as you have removed all of the existing foliage and root system it is then safe to replant with another rose. Others believe that it’s not worth the risk to replant another rose in that area because the virus may still be in the ground. I usually choose to play it safe by replacing the rose with another summer bloomer such as a dwarf crape myrtle or dwarf butterfly bush.