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 Alert East: Pest AlertWest Pest AlertWest odwest.pdf odwest.pdf odwest.pdf odwest.pdf California Oak Mortality Task Force California Oak Mortality Task Force “Minority Report” “Minority Report”

Sudden Oak Death (SOD) Recent epidemic ( present) Recent epidemic ( present) Northern California, southern Oregon Northern California, southern Oregon Dying of oak in urban and forested areas Dying of oak in urban and forested areas Tanoak (Lithocarpus densiflorus) Tanoak (Lithocarpus densiflorus) California Black Oak (Quercus Kelloggi) California Black Oak (Quercus Kelloggi)

Why Worry? Might cause widespread mortality Might cause widespread mortality “New” fungal pathogen in multiple locations – amount of natural resistance uncertain “New” fungal pathogen in multiple locations – amount of natural resistance uncertain Large number of susceptible species, especially nursery plants Large number of susceptible species, especially nursery plants Could spread quickly Could spread quickly Unknown vector(s) of disease transmission Unknown vector(s) of disease transmission Difficult to identify Difficult to identify On nursery plants On nursery plants >$28 million government funding >$28 million government funding UC Berkeley

Management Natural Regeneration Natural Regeneration Wildlife Wildlife Fuel wood Fuel wood Pulp Pulp Shade Trees Shade Trees Black Oak Tanoak

Tanoak Adaptations Range: Native to Oregon and California Range: Native to Oregon and California Climate: Hot dry summers and cool moist winters Climate: Hot dry summers and cool moist winters Soils: Prefer deep and well drained soils Soils: Prefer deep and well drained soils Disturbance: Very susceptible to fire Disturbance: Very susceptible to fire Regeneration: Sprout prolifically after fire or harvest Regeneration: Sprout prolifically after fire or harvest Shade tolerant Shade tolerant Most common hardwood in CA & OR Coast Ranges Most common hardwood in CA & OR Coast Ranges Best adapted to Humboldt & Mendocino Counties (northern CA coast) Best adapted to Humboldt & Mendocino Counties (northern CA coast)

Other Susceptible Species Total of 31 species affected Total of 31 species affected Rhododendron most important Rhododendron most important Two types of hosts: Two types of hosts: Bark canker hosts: e.g. California black oak and tanoak Bark canker hosts: e.g. California black oak and tanoak Foliar hosts: e.g. tanoak Foliar hosts: e.g. tanoak

Symptoms: Bark Canker Sunken cankers on mature trees Sunken cankers on mature trees Produce reddish-brown to tar-black viscous seep Produce reddish-brown to tar-black viscous seep Seeping is the most reliable symptom Seeping is the most reliable symptom

Symptom: Oak Death Canker girdles stem Canker girdles stem Sudden simultaneous leaf death on a major stem or entire tree (“Sudden Oak Death”) Sudden simultaneous leaf death on a major stem or entire tree (“Sudden Oak Death”)

Symptom: Leaf & Shoot Blight Most common symptom, especially on Rhododendron Most common symptom, especially on Rhododendron

Impact on Oaks Oak mortality has reached “unprecedented levels,” but can’t find how much Oak mortality has reached “unprecedented levels,” but can’t find how much Distribution is patchy but 40%-80% of a stand can be impacted Distribution is patchy but 40%-80% of a stand can be impacted

Pathogen: Overview of Phytopthora Species Adapted to areas with high moisture Adapted to areas with high moisture Reproduce both sexually and asexually Reproduce both sexually and asexually Has spore stages that can survive for extended periods, even in adverse conditions Has spore stages that can survive for extended periods, even in adverse conditions

Pathogen: Phytopthora ramorum Timeline: Timeline: Described in Europe – 1993 Described in Europe – 1993 Identified in California – 1999 Identified in California – 1999 Difficult to Identify Difficult to Identify Approximately 60 similar species Approximately 60 similar species No single symptom is adequate for diagnosis No single symptom is adequate for diagnosis

Fungal Pathogen Signs No visible signs No visible signs Two methods available to identify P. ramorum Two methods available to identify P. ramorum Culture fungus from the border of an active infection Culture fungus from the border of an active infection Amplify DNA using polymerase chain reaction (PCR) Amplify DNA using polymerase chain reaction (PCR)

Where Found, What’s at Risk Coast of northern California Coast of northern California Potential to spread Potential to spread Further up west cost Further up west cost Moderate, moist climates in east Moderate, moist climates in east USFS Photo

Life Cycle of Phytopthora ramorum

Life Cycle Zoospores infect host Zoospores infect host short lived and motile short lived and motile asexual asexual swim several feet swim several feet Chlamydospores Chlamydospores Go dormant Go dormant Can survive environmental extremes Can survive environmental extremes If land on plant, can germinate and infect If land on plant, can germinate and infect

Environment Favoring Phytophthora Cool temperatures (50-65 F) Cool temperatures (50-65 F) High moisture levels, water films on leaf and bark surfaces High moisture levels, water films on leaf and bark surfaces Proximity of other hosts: (e.g. California bay laurel, Rhododendron, Madrone,) Proximity of other hosts: (e.g. California bay laurel, Rhododendron, Madrone,) Forest edges with broad canopies: greater likelihood of spores intercepting tree crowns Forest edges with broad canopies: greater likelihood of spores intercepting tree crowns

Predisposing Factors Related to Degree of Stress Fog Fog Precipitation & temperature Precipitation & temperature El Nino effects? El Nino effects? Strong La Niña El Niño El Niño El Niño Moderate El Niño Strong El Niño La Niña La Niña El Niño And La Niña Years: A Consensus List

Predisposing Factors Related to Tree Species Adaptations to Fungus Largely unknown Largely unknown P. ramorum is considered very aggressive; can infect and kill healthy trees. P. ramorum is considered very aggressive; can infect and kill healthy trees. However, However, Symptoms appeared simultaneously over a large area Symptoms appeared simultaneously over a large area Most severe on tan oak outside of preferred habitat Most severe on tan oak outside of preferred habitat “Minority Report” “Minority Report” vations/tanoak.html vations/tanoak.html

Pathogen Movement P. ramorum has been isolated in firewood, leaves, nursery stock, soil, stream water, and rain splash. 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 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 Local spread of disease may be due to infested soil and rain splash Insects and/or birds as vectors? Insects and/or birds as vectors?

Tan oak abundance affected by land use history Stems die easy; roots don’t die: 1000 yr old Stems die easy; roots don’t die: 1000 yr old Regenerated after widespread cutting (after 1930?) Regenerated after widespread cutting (after 1930?) Now mature Now mature Fire exclusion Fire exclusion Increased density and high competition Increased density and high competition Tan oak stands have been predisposed to diseases and secondary pests Tan oak stands have been predisposed to diseases and secondary pests

Predisposing Factors Presence of P. ramorum Presence of P. ramorum Presence of vulnerable hosts: Maturing tanoak on disturbed sites Presence of vulnerable hosts: Maturing tanoak on disturbed sites Presence of alternate hosts (e.g. Rhododendron, California bay laurel) Presence of alternate hosts (e.g. Rhododendron, California bay laurel) Rain/fog belt: geographic area within 50 miles of coast Rain/fog belt: geographic area within 50 miles of coast Excessive rainfall Excessive rainfall

Contributing Factors Beetles: Populations have exploded in recent years, usually attacking severely stressed, dying or dead trees Beetles: Populations have exploded in recent years, usually attacking severely stressed, dying or dead trees Western Oak Bark Beetle (Pseudopityophthorus pubipennis)*** Western Oak Bark Beetle (Pseudopityophthorus pubipennis)*** Oak Ambrosia Beetle (Monarthrum scutellare) Oak Ambrosia Beetle (Monarthrum scutellare) Minor Oak Ambrosia Beetle (Monarthrum detinger) Minor Oak Ambrosia Beetle (Monarthrum detinger) Fungus: Associated with dead oaks and tanoaks Fungus: Associated with dead oaks and tanoaks Hypoxylon thourarsianum Hypoxylon thourarsianum Drought: Weakens infected trees further Drought: Weakens infected trees further

Control Options: Preemptive Harvest Layout Harvest Layout Avoid in infected areas, especially during wet periods. Avoid in infected areas, especially during wet periods. Sanitation Sanitation Wash stations Wash stations Shoes, vehicles, machinery, etc. Shoes, vehicles, machinery, etc. Before and after entering uninfected areas Before and after entering uninfected areas Education and Communication Education and Communication Focus on locations of infected areas and possible modes of dispersal Focus on locations of infected areas and possible modes of dispersal

Quarantines

Reactive Measures Prune infected branches and destroy Prune infected branches and destroy Cut and Burn Cut and Burn Chemical Control Chemical Control Agri-fos Agri-fos Phosphate based Phosphate based Inject or spray Inject or spray Shade trees only Shade trees only No Action No Action

Conclusions Sudden oak death Sudden oak death Name is bad science – not descriptive Name is bad science – not descriptive Great for publicity Great for publicity The disease is complex The disease is complex Moisture is key predisposing factor Moisture is key predisposing factor Stressed trees probably important predisposing factor Stressed trees probably important predisposing factor Pathogen will spread Pathogen will spread Been in forest for years? Been in forest for years? Efforts to prevent spread of pathogen should continue Efforts to prevent spread of pathogen should continue Because of cold climate, doubt that pathogen will get established in Northeast. Lacks fog belt, too. Because of cold climate, doubt that pathogen will get established in Northeast. Lacks fog belt, too.