See the tables for rose varieties resistant to certain diseases. For other resistance information, refer to variety descriptions in plant guides and seed catalogues. Irrigate in the early morning so that plants dry off quickly. Rather than misting, raise humidity by setting pots on trays containing wet sand or gravel, mist the floor of a greenhouse, or install a humidifier. Avoid spreading infections on tools or hands, through splashed water.
Preventive steps are important because once diseases are present they are very difficult to control.
Information in this chapter is intended only as a guide. Always apply pesticides according to directions on the label. Description Small to large circular black spots with fringed margins found on leaves. Choose a planting site in full sun, ensure good air circulation by spacing and pruning, avoid wetting foliage during watering and water early in the day. In the fall, prune seriously affected roses to within 10-15 cm of the graft union to remove overwintering spores within cane tissue.