Trellis Rust (European Pear Rust)

You'll see bright orange leaf spots on pears in spring, with acorn-shaped fruiting structures on leaf undersides. Gymnosporangium sabinae requires both pear and juniper as alternate hosts. The disease is now common on ornamental pears in western Washington. Remove junipers within 1,000 feet of valued pears, or remove pears if junipers are preferred. No chemical controls are practical.

Rust fungi often need two different host plants to complete their life cycle, so identifying and managing the alternate host can break the cycle. Remove heavily infected leaves and dispose of them away from the garden. Improve air circulation to speed leaf drying after rain. Fungicide applications are most effective as preventive treatments before symptoms appear; once pustules are visible, the current infection cycle is already underway.