Powdery mildew on currant shoots
The disease increases in cool, humid, and rainy periods during the spring and early summer.
Tips of young shoots are attacked and may become distorted. Both sides of the leaf can be covered with the white mycelium which turns rusty brown with age. Leaves and berries in all stages of development can be attacked. Edges of leaves can turn brown and black. Severe infection reduces shoot growth and adversely impacts the following year's crop.
See: Powdery mildew whole plant symptoms
See: Powdery mildew fruit symptoms
See: Additional photos and control information from Oregon State University