Rose Rosette, it sounds like it could be something interesting or pretty. Unfortunately, there is nothing pretty about Rose Rosette. It is a disease that attacks roses, causing distorted clusters of growth, eventually leading to near certain death. A viral disease of roses, Rose Rosette Disease (RRD) is spread by insect-like, microscopic eriophyid mites.
Symptoms
One symptom of the disease is distorted clusters of growth called ‘witch’s brooms’. These ‘witch’s brooms’ are often very noticeably red in color on most types of roses, standing out from the rest of the nearby plants. On hybrid tea roses and some others they may be lime colored. Infected canes often have an abundance of thorns which are usually soft and rubbery.
There is no cure for Rose Rosette Disease. In some rare cases, if caught very early, the infected cane can be pruned out with little effect to the remaining plant. Unfortunately, if the disease has been present undetected for any amount of time, the disease is systemic and has spread through the entire plant. If the plant is infected, it is capable of infecting other nearby plants.
Unfortunately, RRD seems to attack all varieties of roses, even the ‘disease resistant’ varieties such as ‘Drift’ and ‘Knockout’.
Recommendations
If you find Rose Rosette Disease on your roses, the best recommendation is to remove the rose, place it in a plastic bag and put it in with your household trash for disposal. It is a lot cheaper and easier to remove and replace one or two roses than to let them infect more, increasing your replacement costs and the amount of inoculum to infect others nearby.
Multiflora rose or the common ‘wild rose’ is a common carrier of the disease and it, unfortunately, is everywhere. Multiflora rose is the major source of inoculum of RRD on cultivated roses.
Preventing RRD on your roses
Frequent monitoring is absolutely key to preventing major losses due to RRD. The disease can often be stopped in its tracks by removing the infected rose as soon as it is noticed. An infected plant left in place becomes the ‘Typhoid Mary’ of your garden, spreading its disease among all of your favorite roses. If you are unsure, call us and we’ll come out and do a thorough evaluation.
Winter pruning is a way to effectively reduce the overwintering eriophyid mite population in your rose garden. The mites tend to hide at the axils of the leaves where the petiole (leaf stem) is attached to the cane on the upper parts of the plant. By pruning hard in the winter, we are not only promoting good and proper growth, but we are also eliminating many of the disease spreading mites when they are the least active.
Removal of any multiflora roses growing within 100 yards of cultivated roses is highly recommended to significantly reduce the amount of disease inoculum present and will increase the chances of maintaining a disease free rose garden.
A good Rose Management Program can also help to reduce the populations of eriophyid mites on your plants. Although this is not a 100% effective strategy, combined with good monitoring and winter pruning you should be able to keep a full garden of roses healthy and blooming for years to come with minimal issues.
Prior to this year, I hadn’t heard of RRD. The following pictures are from Knockout roses at my house. Now that I have been made aware of this disease, I am noticing it throughout our service area. It’s been known since the 1940’s, but for some reason it now seems to be exploding. Perhaps favorable conditions for the vector eriophyid mite populations or a strange weather event that spread infected mites? Either way, we need to be vigilant in preventing the spread of this disease to our beautiful and beloved cultivated roses.
Notice how the ‘witch’s brooms’ stand out from the rest of the plants. The tips are noticeably red while it turns to a light lime green vs. the darker green foliage on unaffected canes or plants.
Closer shot of ‘witch’s broom’. Notice the contrast to the normal, dark green leaves.
Staining in the vascular system of a removed cane. A good indicator that the disease is not just isolated to this cane, but is systemic throughout the plant. Recommendation for this plant is, unfortunately, removal/disposal.