Heavily infected leaves may fall prematurely, increasing the plants susceptibility to winter injury. Leaf spot symptoms are often confused with similar symptoms of raspberry anthracnose. To differentiate these two diseases, examine the stems closely for lesions, which indicate the presence of raspberry anthracnose. Powdery mildew usually appears on the bottom side of leaves as a white to gray powdery growth. This disease may occur yearly, but is not considered a serious problem.
Rust fungi appear on the upper and lower leaf surface as orange-yellow spots.
Several rust fungi commonly infect the leaves and canes, while only a few fungi are able to infect fruit. Rust fungi are fairly common, but do not typically affect the overall health of the plant. However, one fungus, commonly known as orange rust, is considered a serious threat to black raspberries. Red raspberries are immune. Orange rust is a systematic disease that survives winter in newly formed roots, causing new infections the following year.