Michelle Grabowski, UMN Extension Educator
M.Grabowski, UMN Extension
Photo 1: Late Leaf Rust on Red Raspberry
Bright orange powdery spots on red or purple raspberry leaves are symptoms of late leaf rust, a fungal disease caused by Pucciniastrum americanum
. This pathogen can also infect individual druplets in the fruit, turning them into small bright orange powdery masses on an otherwise delicious looking fruit. Late leaf rust needs to alternate between raspberry and white spruce trees. It does not survive on raspberry plants from year to year. Removing nearby white spruce trees is not an effective way to control this disease, however, as spore can travel long distances on the wind. High humidity in Minnesota this summer has favored infection with late leaf rust.