Phytophthora ramorum (Ramorum Blight / Sudden Oak Death)
Phytophthora ramorum
0 host plants · Oomycete
Last updated
Quick Reference
Management
Fall through spring (October-May) during cool, wet periods when leaf wetness persists. Peak infection risk during repeated rain events with daytime temperatures of 50-65°F. Dormant during hot, dry summers (June-August in PNW). In nursery environments with overhead irrigation, year-round risk exists. In southwest Oregon forest settings, peak disease pressure May-October when tanoak is in active growth. # Sources: PNW Plant Disease Management Handbook; OSU Extension
Cool temperatures (50-65°F optimal); persistent leaf wetness from rain, overhead irrigation, or fog; high humidity and dense vegetation; free water required for zoospore dispersal and leaf infection. Sporangia production peaks during cool, wet periods. The pathogen is a cool-weather specialist favored by coastal fog and maritime climates. Rarely establishes in hot, dry regions. # Sources: PNW Handbooks; Wikipedia
Cultural Controls
- Purchase plants from certified nurseries only
- Inspect new plants before purchase; avoid plants with leaf blight, severe leaf loss, shoot dieback, or that have been sitting in standing water
- Quarantine new plants for 4-6 weeks before adding to the landscape
- Avoid overhead irrigation; use drip irrigation and space plants for air circulation
- Remove and destroy infected leaves, blighted shoots, and cankered branches promptly; disinfect tools between cuts
- Do not transport firewood, plant material, or soil from infested areas in California or southwest Oregon
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