Rain can damage rose bushes in a few different ways. Hard-driving rain can bend or break small canes, tear leaves, rot open blooms and over saturate the soil. Repeated heavy rains and very high humidity can also create ideal conditions for fungus such as black spot to take hold. Judicious pruning, cleanup and treatment with fungicides, when warranted, are the chief solutions to rain-damaged bushes.
Cut away any damaged foliage, flowers and canes with clean sharp secateurs. Leave as many healthy leaves as possible to reduce stress on the plant. Cut damaged canes down to a healthy point and place the cut on the bias at least a quarter inch above a leaf axil or bud.
Clean up all of the cuttings that dropped or washed onto the soil by the rains and compost them or discard them in the waste. Leave a clear soil surface to prevent disease from breeding in the debris.
Refrain from watering for a least a week and longer if the soil remains saturated. While roses consume a large amount of water, wet feet are not desirable and simply add more stress on the bush. Do not let the soil dry out entirely but hold off on watering until the first 2 inches of soil dry out before resuming your watering regimen.
Counteract black spot fungus or mold on your roses by spraying with a fungicide approved for use on roses. Spray over the affected foliage according to the package label directions, repeating applications as needed to eradicate or control the condition.