There are few gardening problems more disheartening than a rose disease. Curling, distorted leaves, unusual colored spots, powdery substances--all can have even the most experienced rosarian reaching for the gardening books. Plants, like people, can get sick, for any number of reasons. If you grow roses, certain diseases are more common than others. Knowing how to identify them is a big step toward curing them.
Blackspot is a very common rose disease and most prevalent in areas with a lot of rain and high humidity. You will be able to diagnose blackspot by looking for small circular, yes, black spots on the top of the leaves of the bush. There may be a faint yellow circle surrounding the spot. In the later stages of the disease, the leaves will turn yellow and drop off. This disease can weaken the entire plant enough that it may not survive the winter. There are several fungicides registered for the control of blackspot. Consult with your cooperative extension to find out which one works best in your area.
Powdery mildew is another common disease caused by fungus. This disease will be most evident on new leaves which will become curled and covered in what appears to be a white powder. Horticulturists at Mississippi State University suggest that you might want to try spraying the bush with a mixture of one tablespoon of baking soda and one tablespoon of sunflower oil to one gallon of water, every five to seven days.
Yet another fungus disease that attacks in cool, humid weather. Symptoms of rust are easy to spot: orange powder on the undersides of leaves. Eventually, the disease will spread to the tops of the leaves and they may wilt and eventually drop off. The use of fungicides is recommended for rust.