Diagnose problem with Thornless Hawthorne
There are several rust fungi that show up on hawthorn and other members of the Rosaceae family. Infected leaves have bright orange, yellow or red spots. Infected fruit are covered with small tube-like fungal structures, that pour out large quantities of powdery orange fungal spores. Cedar apple rust, hawthorn rust and quince rust are all caused by fungi in the genus Gymnosporangium. The Gymnosporangium rust fungi rarely cause damage to the health of trees and shrubs in Minnesota, so no management is needed. You can prune and remove infected twigs or branches on Rosaceae plants when they occur.The following links have more information: https://www.extension.umn.edu/garden/yard-garden/trees-shrubs/cedar-apple-rust-and-gymnosporangium-r.