There are four different types of rose bush diseases that can be caught early to save the plant from further damage. Although the diseases are fungal, they do take some time to clear up. You need to know what to look for and what to do to clear up the disease quickly.
The botrytis disease will attack the canes and leaves of the rose bush.and will prevent blooms from opening. Any flowers or buds that are infected will appear shriveled and grayish brown in color. The plant must be pruned to get rid of the dead and diseased parts. Apply micronized sulfur to the soil to prevent further damage to the plant. Rose bushes that are under stress will be more susceptible to the botrytis disease.
Rose bushes that look as if they have been sprinkled with baby powder could have powdery mildew, which can cause the leaves to turn brown or yellow. It will make the flowers and shoots look disfigured. Proper air circulation can prevent this disease from attacking rose bushes. However, if the bush does have powdery mildew, apply a mixture of 1/2 tsp vegetable oil, 1 tsp baking soda and 1 quart of warm water a spray bottle to get rid of the disease.
The rose bush that has black spots on the leaves could have fallen prey to black spot. In most cases, the disease is the result of an injury during winter. The disease is hard to control, but a dose of sulfur every week will clear up the disease. Just sprinkle the sulfur around the soil at the base of the plant. Remove debris and damaged foliage. apply mulch to the base of the bush in fall to prevent this disease from reoccurring.
Pruning the rose bush and leaving a wound on the stem can cause the disease canker. The disease can spread through dirty pruning tools, splashing water or insects. Remove any parts of the plant that have become infected and use a copper based fungi controller to stop the disease. Note: Do not do anymore pruning or fertilizing of the rose bush, except for cutting the infected parts, until the canker is cleared or the disease can spread.
Rust spreads during the winter as black spot does. It lives in the leaf buds and spores can blow to other plants in windy conditions. The disease leaves little orange spots on the backside of the leaves. Remove all infected parts of the plant and use mulch around the base of the rose bushes to prevent rust. Remove all debris on the ground around the plant.