- Along with the beauty of roses come their enemies, aphids, slugs, and Japanese beetles. Roses are also susceptible to fungi, bacteria and viruses. One of the worst forms of fungus is rose rust. If it is not handled quickly it can kill young rose bushes. The first signs are powdery yellow, orange-reddish warty spots on the underside of the leaves. It then spreads to the woody stalks of the bush and the upper part of the leaves as the condition worsens. Eventually the wart-like spores turn a dark brown and the leaves die and fall to the ground.
- Rose rust is mostly predominant in the northwestern Pacific coast regions of the U.S., but it can appear in other areas. This fungus prefers an ongoing wet condition above 55 degrees and under 85 degrees. This fungus is spread by the wind. The prolonged moisture of fog, rain and dew assist the fungus spores in entering the rose tissues. Even if the diseased rose bushes died and were left over the winter, they would produce new spores in the spring. It's a good chance that any new rose bushes planted in the location or even in the same area would be infected with rose rust.
- When rose rust is first detected, you must cut the diseased leaves and stalks off and take them out of the rose bush area. They must be disposed of and not included in a compost pile where they can continue to grow. A good prevention technique is to spray a fungicide containing lime-sulfur, directly on the plant, in the early spring when the rose bush is still dormant. If you were too late in catching the rose rust condition, in the fall, rake up all leaves and destroy them. Spray the rose bushes with the same fungicide to kill left over spores that might survive the winter.
