Cluster Cup Rust
Cluster cup rust on Ribes americanum Mill. Top arrow indicates infected developing fruit;
bottom arrow indicates rust aecial pustule on leaf.
Cluster cup rust on leaves and inflorescence of Ribes americanum Mill.
Black arrows indicate leaf pustules, white arrow indicates abnormal rust-infected fruit
Cluster cup rust produces yellow spots on leaves, flowers and developing fruits in April and May. The affected Ribes are usually growing in a low lying area, possibly near a swamp. The alternate hosts for this disease are Ribes and sedges. This disease can significantly reduce the yield of black fruited currants. This disease can be significant in the mid-west and northern plain states.