All roses are susceptible to disease, including old-fashioned, or antique roses, and long stem hybrid tea roses, known as florist roses. Rose diseases can appear because of poor air circulation around the plants, geographic location or the variety of rose. The best prevention is finding what rose diseases are most common in your area and planting roses resistant to those diseases. Contact your local county agricultural extension office for recommended varieties for your area.
There are several different kinds of powdery mildew, but they all look the same. Plants infected with powdery mildew look like they were dusted with white talcum powder. It does not need water, warm weather or humidity to spread. Once it covers the leaves, it interferes with photosynthesis, and the leaves shrivel and fall off. If a plant continues to be affected, it may eventually die from the disease. Powdery mildew spreads by the wind, so other plants can become infected once it appears in the garden.
Rust appears as brown or orange spots on the underside of leaves. Damage to the health of the plant occurs when the disease is uncontrolled. Infected leaves eventually fall off, which weakens the plant. The spores remain viable on the fallen leaves. The disease is spread by wind and splashing water.
Black spot is easy to identify because of the numerous black spots that appear on the leaves of rose bushes. The leaves often turn yellow and fall off the infected plant. Once black spot infects the leaves of one plant, it can spread to other plants. Black spot can overwinter on fallen leaves that remain around the base of the plant during the winter and reinfect the plant in the spring. Transmission to the plant is accomplished by splashing water that occurs during a typical rain storm or from overhead watering. Black spot often lives in compost and mulches that are exposed to infected rose bush leaves.
Botrytis blight shows up on new rose bush plantings in early spring because it thrives in cool, moist weather and favors stressed plants. It can be seen as a fuzzy gray growth inside stunted, brown and damaged flowers.