Trellis Rust (European Pear Rust)
Gymnosporangium sabinae
1 host plant · Fungal
Last updated
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. 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.
Quick Reference
Management
Juniperus (telial host): telia present March-May during spring wet season. Pear hosts: susceptible during bloom period (April-May in western Washington/Oregon) through early summer leaf emergence. Aecia develop on pear leaves June-September and release spores through fall. (Source: PNW Plant Disease Management Handbook, Trellis rust distribution history)
Wet spring weather at temperatures 50-65°F triggers telia swelling and basidiospore release from Juniperus galls. Infection of pear occurs when spores land on susceptible tissue (leaves, fruit, twigs) in spring-early summer. Cool, moist conditions favor infection. (Source: PNW Plant Disease Management Handbook)
Cultural Controls
- Eliminating either host is the only practical cultural control.
- If pear is the important plant, remove all juniper from a 1,000-ft radius.
- Separating hosts by 0.5 to 2 miles has been recommended.
Gymnosporangium sabinae (trellis rust) was first confirmed in North America in the Bellingham, WA area in 1997 and has since spread throughout western Washington. It appeared in western Oregon starting in 2016. As of 2018, it has not been a commercial problem in PNW orchards but commonly affects ornamental pear in residential landscapes.