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. To properly manage fungal diseases, begin with the cultural practices previously listed. Fungicide control is available for anthracnose, cane blight, and spur blight. A dormant season application of lime sulfur can be applied in early spring as the buds begin to swell, but before leaves appear. Sulfur and copper-based fungicides are the only other chemicals available for homeowner use.