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If you have roses, most of you know that many of them can be very disease prone, however the knockout roses are very often disease free. Knockouts aren’t totally full proof. They do still get the occasional assault from insects. There is a disease or more specifically a virus that has become more common in roses over the last several years and it attacks ALL roses! The disease is called rose rosette and as in all plant viruses there is no cure.
Symptoms of rosette include rapid elongation of shoots, reddening of foliage, witches broom (clustering of small shoots), distorted leaves, excessive thorns, deformed buds and flowers, increased susceptibility to other rose diseases especially powdery mildew and lack of winter hardiness.
The rosette virus is generally vectored or carried to roses from a mite called the rose leaf curl mite. These mites are so small they are only visible under a microscope. They can’t fly but they can crawl and blow in the wind to other rose plants. Other ways that roses can be infected with this virus is through mechanical means like pruning and deadheading. The tools carry the virus from one plant to another.
As stated earlier, there is no cure when a rose gets rosette, so if a plant becomes infected you should dig the plant out and destroy it, being careful not to damage other roses in the process. While removing the plant, it is easy to move mites around, if they are present, as well as wound other plants causing transmission of the virus. So again be careful. Do not plant roses in the same place for several years because root pieces can also transmit the virus, as well as mites could still be present in the area.
There has been some research done that if you catch the first infected shoot early enough you can prune it out to the ground and save the overall plant from infection. But this would be a rare occasion that you would catch the infection early enough. By the time most of us notice that the plant looks different it is too late because the disease initially is very similar to herbicide damage as well.
Rose rosette is not all bad because it is reducing the numbers of wild or multiflora roses as well. As a matter of fact the wild roses may be even more susceptible than our garden varieties. But this too comes at a price. The wild roses allow the disease to be more prevalent and the closer they are to your garden roses the more likely you are to get rosette. Ideally you want to destroy any multiflora roses near your property or at least have your roses upwind and at least 100 yards from them.
If you have any questions or have roses you think may have rosette, bring a sample to the office and I will check it out for you.