Everyone has heard the expression to be careful what you wish for. Sometimes a cure for one problem can cause another. Rose rosette disease is a prime example.
Years ago, multiflora rose was planted as natural fencing and for soil conservation in the eastern US. It was also used as a rootstock for ornamental roses. Over the years, multiflora rose became one of the thorniest problems for livestock farmers. It also lowered pasture land value.
When I lived in West Virginia, multiflora rose dominated pastures. Some were so infested that livestock productivity was a fraction of what it could have been. Deer liked to eat them, and these roses provided great cover for deer and rabbits. Most farmers wanted the roses gone and overused pesticides to do so.
The last few times I have driven around in rural West Virginia I have noticed far fewer pastures dominated by multiflora rose. I suspect the major reason might be rose rosette disease.
I remember back in the 80s many agronomists and livestock scientists I worked with were discussing how this disease was reducing rose populations in the Midwest. These guys were interested in pasture and livestock production. They didn’t have much concern about the influence of rose rosette disease on ornamental roses.
However, this disease can be spread on ornamental roses like ‘knock out’ types mechanically through contaminated grafts. It also can be spread from plant to plant through natural root grafts. Likely the most common way the disease spreads is through a tiny mite. This mite transmits a virus. That virus is the major culprit in the demise of the wild multiflora rose population.
Virus diseases cannot be chemically controlled like fungus diseases can. Scientists continue to develop chemicals that can deactivate or inhibit viruses. However, viruses, particularly plant viruses mutate rapidly to overcome this. Basically, chemical control is difficult.
Knock out and other types of landscape roses are becoming increasingly popular. Because of this, I suspect we might be dealing with rose rosette disease more in the future. Roses with rose rosette disease develop clusters of bright red shoots in the spring. We call these clusters witches’ broom. This abnormal growth is easy to spot.
Many virus diseases can be controlled by removing infected tissue back to healthy wood. This is not one of them. Entire plants must be removed from the area or an entire rose planting might be in danger.
Homeowners might wonder what their best course of action might be if they don’t have any signs of this disease yet. I would suggest eliminating any wild multiflora roses that might be nearby. Cutting down canes and treating the surface with concentrated glyphosate seems to be the best method.
The good news is that multiflora roses aren’t very common around here. I know where a few patches are, but in general, interaction between wild and cultivated roses is limited. Still, this disease is something to keep in mind, especially since most roses are grown in areas where wild roses are more common.
Ted Manzer teaches agriculture at Northeastern High School (email@example.com).