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Sudden Oak Death: Is the Sky Falling? (or why I should take INT 256) Prepared by: Mike Maguire, April 2003 Updated by: W.H. Livingston, February 2005 Web Sites Pest Alert East: Pest AlertWest

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sudden oak death is the sky falling or why i should take int 256

Sudden Oak Death:Is the Sky Falling?(or why I should take INT 256)

Prepared by: Mike Maguire, April 2003

Updated by: W.H. Livingston, February 2005

web sites
Web Sites
  • Pest Alert East:
  • Pest AlertWest
  • California Oak Mortality Task Force
  • “Minority Report”
sudden oak death sod
Sudden Oak Death (SOD)
  • Recent epidemic (1995 - present)
  • Northern California, southern Oregon
  • Dying of oak in urban and forested areas
    • Tanoak (Lithocarpus densiflorus)
    • California Black Oak (Quercus Kelloggi)
why worry
Might cause widespread mortality

“New” fungal pathogen in multiple locations – amount of natural resistance uncertain

Large number of susceptible species, especially nursery plants

Could spread quickly

Unknown vector(s) of disease transmission

Difficult to identify

On nursery plants

>$28 million government funding

Why Worry?

UC Berkeley



Black Oak

  • Natural Regeneration
    • Wildlife
    • Fuel wood
    • Pulp
  • Shade Trees
tanoak adaptations
Tanoak Adaptations
  • Range: Native to Oregon and California
  • Climate: Hot dry summers and cool moist winters
  • Soils: Prefer deep and well drained soils
  • Disturbance: Very susceptible to fire
  • Regeneration: Sprout prolifically after fire or harvest
  • Shade tolerant
  • Most common hardwood in CA & OR Coast Ranges
  • Best adapted to Humboldt & Mendocino Counties (northern CA coast)
other susceptible species
Other Susceptible Species
  • Total of 31 species affected
  • Rhododendron most important
  • Two types of hosts:
    • Bark canker hosts: e.g. California black oak and tanoak
    • Foliar hosts: e.g. tanoak
symptoms bark canker
Symptoms: Bark Canker
  • Sunken cankers on mature trees
  • Produce reddish-brown to tar-black viscous seep
  • Seeping is the most reliable symptom
symptom oak death
Symptom: Oak Death
  • Canker girdles stem
  • Sudden simultaneous leaf death on a major stem or entire tree (“Sudden Oak <Leaf> Death”)
symptom leaf shoot blight
Symptom: Leaf & Shoot Blight
  • Most common symptom, especially on Rhododendron
impact on oaks
Impact on Oaks
  • Oak mortality has reached “unprecedented levels,” but can’t find how much
  • Distribution is patchy but 40%-80% of a stand can be impacted
pathogen overview of phytopthora species
Pathogen: Overview of Phytopthora Species
  • Adapted to areas with high moisture
  • Reproduce both sexually and asexually
  • Has spore stages that can survive for extended periods, even in adverse conditions
pathogen phytopthora ramorum
Pathogen: Phytopthora ramorum
  • Timeline:
    • Described in Europe – 1993
    • Identified in California – 1999
  • Difficult to Identify
    • Approximately 60 similar species
    • No single symptom is adequate for diagnosis
fungal pathogen signs
Fungal Pathogen Signs
  • No visible signs
  • Two methods available to identify P. ramorum
    • Culture fungus from the border of an active infection
    • Amplify DNA using polymerase chain reaction (PCR)
where found what s at risk
Where Found, What’s at Risk
  • Coast of northern California
  • Potential to spread
    • Further up west cost
    • Moderate, moist climates in east

USFS Photo

life cycle
Life Cycle
  • Zoospores infect host
    • short lived and motile
    • asexual
    • swim several feet
  • Chlamydospores
    • Go dormant
    • Can survive environmental extremes
    • If land on plant, can germinate and infect
environment favoring phytophthora
Environment Favoring Phytophthora
  • Cool temperatures (50-65 F)
  • High moisture levels, water films on leaf and bark surfaces
  • Proximity of other hosts: (e.g. California bay laurel, Rhododendron, Madrone,)
  • Forest edges with broad canopies: greater likelihood of spores intercepting tree crowns
predisposing factors related to degree of stress
Predisposing Factors Related to Degree of Stress
  • Fog
  • Precipitation & temperature
    • El Nino effects?

El Niño And La Niña Years: A Consensus List

predisposing factors related to tree species adaptations to fungus
Predisposing Factors Related to Tree Species Adaptations to Fungus
  • Largely unknown
  • P. ramorum is considered very aggressive; can infect and kill healthy trees.
  • However,
    • Symptoms appeared simultaneously over a large area
    • Most severe on tan oak outside of preferred habitat
  • “Minority Report”
pathogen movement
Pathogen Movement
  • P. ramorum has been isolated in firewood, leaves, nursery stock, soil, stream water, and rain splash.
  • Long distance spread may be due to human movement of infested host materials
  • Local spread of disease may be due to infested soil and rain splash
  • Insects and/or birds as vectors?
tan oak abundance affected by land use history
Tan oak abundance affected by land use history
  • Stems die easy; roots don’t die: 1000 yr old
  • Regenerated after widespread cutting (after 1930?)
  • Now mature
  • Fire exclusion
    • Increased density and high competition
  • Tan oak stands have been predisposed to diseases and secondary pests
predisposing factors
Predisposing Factors
  • Presence of P. ramorum
  • Presence of vulnerable hosts: Maturing tanoak on disturbed sites
  • Presence of alternate hosts (e.g. Rhododendron, California bay laurel)
  • Rain/fog belt: geographic area within 50 miles of coast
  • Excessive rainfall
contributing factors
Contributing Factors
  • Beetles: Populations have exploded in recent years, usually attacking severely stressed, dying or dead trees
    • Western Oak Bark Beetle (Pseudopityophthorus pubipennis)***
    • Oak Ambrosia Beetle (Monarthrum scutellare)
    • Minor Oak Ambrosia Beetle (Monarthrum detinger)
  • Fungus: Associated with dead oaks and tanoaks
    • Hypoxylon thourarsianum
  • Drought: Weakens infected trees further
control options preemptive
Control Options: Preemptive
  • Harvest Layout
    • Avoid in infected areas, especially during wet periods.
  • Sanitation
    • Wash stations
    • Shoes, vehicles, machinery, etc.
    • Before and after entering uninfected areas
  • Education and Communication
    • Focus on locations of infected areas and possible modes of dispersal
reactive measures
Reactive Measures
  • Prune infected branches and destroy
  • Cut and Burn
  • Chemical Control
    • Agri-fos
    • Phosphate based
    • Inject or spray
    • Shade trees only
  • No Action
  • Sudden oak death
    • Name is bad science – not descriptive
    • Great for publicity
  • The disease is complex
    • Moisture is key predisposing factor
    • Stressed trees probably important predisposing factor
    • Pathogen will spread
    • Been in forest for years?
  • Efforts to prevent spread of pathogen should continue
  • Because of cold climate, doubt that pathogen will get established in Northeast. Lacks fog belt, too.