Growing Roses - Insects and Diseases Growing Roses in Iowa Insects and Diseases Diseases.
Sanitation is the best method of reducing problems that can arise once roses are established.
The main rose diseases are black spot, stem canker and powdery mildew. Black spot symptoms are irregular black spots often surrounded by a yellow halo. As infection progresses, leaves eventually drop. Leaf drop contributes to the spread of the disease by harboring spores and results in weakening the plant and increasing susceptibility to winter injury, drought, dieback and stem cankers. Flower production will be reduced if the disease is allowed to spread.