Roses under stress will be highly susceptible to this disease. Blackspot disease is more common on some of the old fashioned rose varieties. Blackspot also is favored by wet weather and 65-75 degree F temperatures. Severe infections will cause defoliation. Rose Mosaic , caused by a virus, is found worldwide.
Symptoms vary, but usually show up as mosaic patterns or splotches of yellow and green.
No adverse effect on flower production has been reported, but leaf symptoms may detract form the overall quality of the plant. Infected plants may be more sensitive to winter kill. The only way to control rose mosaic is to remove infected plants. Because of no adverse effect on flowering, most people leave the plants alone and ignore the virus. Disease Controls Most rose diseases can be controlled or prevented with simple maintenance or cultural practices.