Roses are popular, deciduous plants that grow as small trees, shrubs and vines. These finicky flowers demand plenty of attention and reward their growers with plentiful blooms and unforgettable fragrances. Although roses can be stunning, these plants are susceptible to a wide array of diseases, many of which can be damaging, if not fatal, to the rose. Gardeners that choose to take on the rose challenge must be willing to defend their plants throughout the entire year.
Powdery mildew is a common and serious disease of the rose plant family. This fungal disease can affect the new and old foliage of the rose, as well as the bud, shoots and blooms of the rose itself. The mildew initially develops on the foliage of the rose, covering it with a powdery white fungus. Progression of the disease causes dieback and growth stunt of newly developing buds. Shoots and flowers grow distorted and stunted. Severely infected areas of the rose plant will defoliate prematurely. Powdery mildew can be controlled with a regular fungicidal treatment.
Black spot is a water-dependent disease. The University of Maine Cooperative Extension explains that, for these fungal spores to germinate, they must remain wet for at least seven hours. The germinated spores are then transported by rain and wind onto the rose plant where it develops rapidly during periods of warm temperatures. Infected rose plants develop small, black spots on the foliage. The infected foliage also develops a yellowing near the black spots. This yellowing spreads across the foliage as the disease progresses. Rose plants that are infected with black spot experience premature defoliation and cane dieback. Fungicidal treatments are effective in preventing and controlling this disease.
Like many fungal diseases, rose rust is spread by fungal spores. These fungal spores commonly infect the foliage of rose plants, but can infect the developing stems and sepals as well. Rose plants will first show symptoms on the foliage. The infected foliage develops powdery, orange boils on the underside of the leaves that create yellowish-orange spots on the upper surfaces. The spread of the disease causes these spots and pustules to appear on the stems and sepals. These areas become distorted and begin to curl. Continued progression of rose rust causes necrosis of the infected areas. The disease can be controlled with a combination of pruning and fungicidal spray treatments.