50+ Lifestyles

What is Wrong With my Roses?

By Martha Smith
University of Illinois Extension

A healthy rose in full bloom is truly an attraction in any garden. Lately, the University of Illinois plant clinic has received discolored and distorted rose samples. The unfortunate diagnosis is Rose Rosette. Rose Rosette disease is caused by what is commonly thought to be a “virus-like” disease that is known to affect plants in the Rose family. Multiflora rose, which has escaped cultivation and is considered invasive, is very susceptible and often is the source for new infections. Rose Rosette is spread by an eriophyid mite, a mite so small you need strong magnification to see them. They feed on an infected plant and then pass it on to the next rose they feed on. Research has also shown that it can be transmitted by grafting. Many of our hybrid roses are grafted.

Unfortunately, there are no tests for this disease so we have to rely on symptoms. Fortunately the symptoms for Rose Rosette are very distinctive. You may see thick, often redder than normal stems with an abnormally high number of thorns. Witches broom growth often appears. This looks like multiple stems growing from the same area often with small, distorted and discolored foliage.

Realize that herbicide damage can look very similar to Rose Rosette. Evaluate what may have been applied recently. Some herbicides can cause witches brooms, distorted growth and discoloration. The difference is herbicides will not cause the prolific thorn production along the stems. Once infected, plants cannot be saved. Plants with symptoms should be completely dug up and destroyed when first noticed so as not to serve as a source of the disease that can be spread by mites. Dig out all the roots if possible. Since mulitflora roses growing in the wild can be infected, try and separate your garden roses as far away from them as possible. Remove them from your property. Mite control is possible, but research suggests the critical application time is May and June. Roses can be replanted since the soil itself is not infected. But any remaining plant parts harbor the disease and can serve as a source for future infections. Watch other roses in the area for any signs of the problem and remove promptly.

This information was reprinted from the University of Illinois Home, Yard & Garden newsletter. For more information, visit http://web.extension.illinois.edu/hmrs.