Prunus necrotic ringspot virus and apple mosaic virus are the principal pathogens. They may be found separately or together in diseased plants.
The leaf symptom is a pattern of light and dark green areas that give a mosaic effect in infected leaves. In roses, only occasional effects on flower production has been reported but foliar symptoms detract from the overall quality. Infected plants tend to be less vigorous than healthy plants and are more sensitive to winter injury. It is not unusual for infected plants to remain symptomless. The degree of symptom expression varies with the cultivar, the time of year, and from year to year. In general, symptoms are more evident in the spring. The entire plant is always infected; however, mosaic symptoms may not show up until the weather turns cool, a condition which favors virus disease development.
No pesticide or cultural control can cure a virus disease. Avoid virus diseases by buying healthy plants. Never purchase plants showing mosaic symptoms. Diseased plants should not be used for propagation. Please contact your local county extension office for current information.