Rose Rosette Disease-What is it and What to do about it
Spring in the Midwest – bees buzzing, flowers blooming, all is right with the world. Suddenly, a bushy clump of red, thorny canes appears and your rosebush is doomed! Cue the Psycho music - fade to black…..
If you grow roses, stories about Rose Rosette Disease can seem like a horror movie. Does it scare you so badly that you refuse to plant roses and want to burn or rip out every rosebush in the neighborhood as if it was a photosynthetic Frankenstein?!? Okay, that’s an exaggerated scenario, but plant diseases can make gardeners reconsider whether susceptible plants are worth the risk. As plant professionals, it is our job to make sure our customers not only have the facts, but clean plants.
What is Rose Rosette?
A virus transmitted by an Eriophyid mite (Phyllocoptes fructiphylus) found exclusively on roses causes rose rosette. These mites are so small that they move from plant to plant primarily via air currents. Since both the mites and the virus are too small to be seen with the naked eye, we look for the disease symptoms to determine whether we have infected plants.
Symptoms of Rose Rosette
How can you tell if your roses are infected? While the symptoms can vary somewhat depending on the variety, several symptoms show up consistently across multiple varieties. Bright red growth should immediately be suspect. Some roses flush red normally but grow out of it. Diseased growth remains excessively red. Rose rosette also causes abnormal growth, including witches brooms with small, distorted leaves, elongated stems and excessively thorny canes. These thorns emerge soft and pliable before hardening off. Symptomatic canes may also be thicker than the parent cane.
Glyphosate (e.g., Round Up herbicide) exposure the previous fall can potentially cause abnormal growth, which can be confused with rose rosette. Very low rates consistent with accidental exposure cause witches brooms, small leaves and distorted growth. However, when glyphosate is the culprit the plants are often more yellow than red. The herbicide also has no effect on the excessive thorn production that is so characteristic of rose rosette. Additional information on how to tell the difference between rose rosette and glyphosate damage is available from the University of Arkansas.
Treatments for Rose Rosette
Suppose you do find rose rosette symptoms, what are your options? There is no cure. What we normally do is rogue and destroy the plant as soon as we see the symptoms to prevent spreading the disease to other roses. New evidence shows that the virus is found only in symptomatic parts of the plant. No symptoms = no virus. So if you find it early, simply cut the plant back several inches below where the disease first appears. Depending on the age and size of the plant, you could even cut it back all the way to the ground. However, if the disease has been present for several years, dig up the plant and remove all the roots you can. Destroy the plant by burning it or placing it in a plastic bag to land fill it. Roses typically live 2-5 years after infection. You could just let it die, but then the rest of your roses could be infected from this one inoculum source.
Can you avoid the heartache of losing your roses? It's possible, preventative measures often work. Get rid of symptomatic roses quickly; don’t just let nature take its course. Eliminate multiflora roses in the area. This is an invasive species that was originally brought to this country in 1866 as a rootstock for grafted roses. Later it was planted for erosion control, as a bird sanctuary and food source, as a living fence for cattle, for strip mine reclamation, and as a crash barrier on highways. Reminds me a little of kudzu – seemed like a good idea at the time. Since the disease vector is an Eriophyid mite, spray your bushes with an approved miticide such as Avid, Akari, Judo or horticultural oil. The tiny creatures hide in cracks, crevices and leaf axils so good coverage is extremely important. Also be aware that not all miticides control Eriophyid mites. Read the label to make sure the product you choose controls Eriophyid mites, also called gall, rust or blister mites.
Prevention practices normally include planting resistant varieties. Unfortunately, rose rosette does not give us that option. No resistant rose varieties have been found, although research is continuing.
For more information, check out the archived webinar presented by Greenhouse Grower and Conard-Pyle.