Pacific Coast Pear Rust
Gymnosporangium libocedri (P
5 host plants · Fungal
Last updated
Pacific coast pear rust affects pear trees and relies on juniper as an alternate host. Pear fruit become malformed while young and drop from the tree. Remove infected alternate hosts around orchards when possible. This rust spreads by spores in wet weather. Improve air circulation and reduce leaf wetness to manage disease spread during vulnerable periods. This rust disease spreads readily in moist spring and fall conditions. Watch foliage closely for early symptoms.
Remove alternate hosts around the orchard. Separating hosts by 0.5 to 2 miles has been recommended. Identify and manage the alternate host if one exists. Remove heavily infected tissue and clean up fallen debris. Preventive fungicide applications before the infection window offer the best chemical control.
Quick Reference
Management
Incense cedar: telia active March through May during spring rains. Rosaceae hosts: susceptible from leaf emergence through bloom (approximately April-May in western Oregon/Washington) and continuing through early summer while new foliage is expanding. Fruit susceptibility is highest during and shortly after bloom. (Source: PNW Plant Disease Management Handbook)
Wet spring weather with temperatures ≥50°F (10°C) triggers telia swelling and basidiospore release from incense cedar. Basidiospore production requires continuous moisture (rain or heavy dew) for telia hydration. Cool, moist conditions (50-65°F / 10-18°C) on deciduous hosts favor infection and aecial development. Telia can re-swell and release additional basidiospores with subsequent rain events throughout spring. (Source: PNW Plant Disease Management Handbook)
Cultural Controls
- Prune and destroy cedar brooms before spring PNW Plant Disease Management Handbook
- Remove alternate hosts from proximity PNW Plant Disease Management Handbook
- Avoid overhead irrigation that wets foliage PNW Plant Disease Management Handbook
- Maintain overall tree health PNW Plant Disease Management Handbook
Less common in Puget Sound lowlands than in the Willamette Valley due to lower prevalence of Calocedrus decurrens as a landscape tree. When incense cedar IS present near pear orchards or home fruit trees, infections can be significant in wet spring years. Orange telia are visible on landscape incense cedars in March-April.
Host Plants (5)
Sources & References
Primary: PNW Plant Disease Management Handbook
- name: "PNW Plant Disease Management Handbook - Cedar, Incense-Broom Rust
- https://pnwhandbooks.org/plantdisease/host-disease/cedar-incense-broom-rust
- name: "OSU Extension Service - Orange rust infects incense cedar and pear trees across Western Oregon
- https://extension.oregonstate.edu/news/watch-out-rust-can-jump-incense-cedars-fruit-trees
- name: "Forest Pathology - Incense Cedar Rust
- https://forestpathology.org/rusts/incense-cedar-rust/
- name: "Wikipedia - Gymnosporangium libocedri
- https://en.wikipedia.org/wiki/Gymnosporangium_libocedri