Sudden Oak Death Is the Sky Falling or

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 n Pest Alert East: n n Pest Alert. West n n http: //www. na. fs. fed. us/spfo/pubs/pest_al/sodwest/pdf /sodwest. pdf California Oak Mortality Task Force n n http: //www. na. fs. fed. us/spfo/pubs/pest_al/sodeast/sod east. pdf http: //nature. berkeley. edu/comtf/html/about_p__ramor um. html “Minority Report” n http: //phytosphere. com/tanoakobservations/tanoak. ht ml

Sudden Oak Death (SOD) Recent epidemic (1995 present) n Northern California, southern Oregon n Dying of oak in urban and forested areas n Tanoak (Lithocarpus densiflorus) n California Black Oak (Quercus Kelloggi) n

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

Managemen t n Natural Regeneration n n Wildlife Fuel wood Pulp Shade Trees Tanoak Black Oak

Tanoak Adaptations n n n n 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 n n n Total of 31 species affected Rhododendron most important Two types of hosts: n n Bark canker hosts: e. g. California black oak and tanoak Foliar hosts: e. g. tanoak

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

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

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

Impact on Oaks n n 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 n n n 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 n Timeline: Described in Europe – 1993 n Identified in California – 1999 n n Difficult to Identify Approximately 60 similar species n No single symptom is adequate for diagnosis n

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

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

Life Cycle of Phytopthora ramorum

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

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

Predisposing Factors Related to Degree of Stress n n Fog Precipitation & temperature n El Nino effects? El Niño And La Niña Years: A Consensus List 1988 -89 Strong La Niña 1989 -90 - 1990 -91 - 1991 -92 El Niño 1992 -93 El Niño 1993 -94 El Niño 1994 -95 Moderate El Niño 1995 -96 - 1996 -97 - 1997 -98 Strong El Niño 1998 -99 La Niña 1999 -00 - 2000 -01 La Niña 2001 -02 -

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

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

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

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

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

Quarantines

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

Conclusions n Sudden oak death n n n The disease is complex n n n Name is bad science – not descriptive Great for publicity 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.