These symptoms could be the result of an infection by a virus. A virus is a submicroscopic disease-causing entity that can only be viewed with an electron microscope. Some symptoms typically associated with viral infections include: distorted and malformed leaves or growing points; stunted growth; a mosaic pattern of light and dark green or yellow on leaves; yellow spotting on leaves; other spots or line patterns on leaves; and cup-shaped leaves. However, virus diseases cannot be diagnosed on the basis of symptoms alone. Some of these symptoms can also be caused by high temperatures, insect-feeding, growth regulators, herbicides, and nutrient deficiencies and excesses. The best way to tell if a virus is infecting a rose is if the same symptoms occur year after year. If the deformed or abnormal growth never disappears, dig out the entire infected plant and replace it. The reason it is necessary to remove the plant is that a virus is systemic - found in all parts of the plant. So, pruning away the afflicted parts will not remove the virus from your rose. There are no chemicals that cure a virus-infected plant or any that protect plants from becoming infected. Your only course of action is to rogue-out the infected plant and discard it.
To guard against virus diseases, consider the following measures:
1. Purchase certified virus-tested or virus-free plants.
2. Maintain strict insect and mite control.
3. Control weeds because they may harbor viruses, mites, nematodes, and insects.
4. Destroy virus-infected plants.
5. Disinfect pruning tools by cleaning them with rubbing alcohol, drying, and spraying with a light coat of oil to prevent rusting.
