Broom Rust
Gymnosporangium libocedri
16 host plants · Fungal
Last updated
This profile contains verified disease data from extension databases. Regional field notes and expert review are in progress.
Bright orange or brown fuzzy pustules appear on leaf undersides, indicating this fungal disease requires two different plant species to complete its entire life cycle. The disease spreads readily by wind-borne spores traveling from alternate hosts to susceptible plants. Remove nearby alternate hosts or susceptible plants to interrupt the disease cycle. Improve air circulation and avoid overhead watering that spreads spores.
Remove and destroy cedar brooms before spring. Remove alternate hosts from around the planting. 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 present March-May during spring rains. Deciduous hosts: susceptible during bloom period (April-May in western Oregon) and through early summer when new foliage emerges. (Source: PNW Plant Disease Management Handbook)
Wet spring weather (≥50°F) triggers telia swelling and basidiospore release from incense cedar. Cool, moist conditions (50-65°F) on deciduous hosts favor aecial development. (Source: PNW Plant Disease Management Handbook; Gymnosporangium lifecycle phenology)
Cultural Controls
- Remove and destroy cedar brooms before spring.
- Remove alternate hosts from around the planting.
- Separating hosts by 0.5 to 2 miles has been recommended.
- Avoid overhead irrigation that wets foliage for extended periods of time.