Gymnoconia interstitialis

Gymnoconia interstitialis, otherwise known as orange rust of raspberries, is a well-known disease of raspberries and blackberries throughout the eastern United States and southern Canada. The disease targets the usefulness of the leaves, attacking them until they die and fall off of the plant. The disease returns annually, and this recurrence essentially makes the plants worthless—rarely do affected plants recover. Some strains have such a strong impact on the plants that the cultivation becomes unprofitable. Hesler & Whetzel (1917) claim, "Ten per cent rusty plants are frequently reported. Twenty-five per cent or more are recorded."...read more on Wikipedia.