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

1. 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

2. Web Sites • Pest Alert East: • http://www.na.fs.fed.us/spfo/pubs/pest_al/sodeast/sodeast.pdf • Pest AlertWest • http://www.na.fs.fed.us/spfo/pubs/pest_al/sodwest/pdf/sodwest.pdf • California Oak Mortality Task Force • http://nature.berkeley.edu/comtf/html/about_p__ramorum.html • “Minority Report” • http://phytosphere.com/tanoakobservations/tanoak.html

3. 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)

4. 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

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

6. 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)

7. 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

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

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

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

11. 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

12. 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

13. 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

14. 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)

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

16. Life Cycle of Phytopthora ramorum

17. 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

18. 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

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

20. 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” • http://phytosphere.com/tanoakobservations/tanoak.html

21. 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?

22. 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

23. 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

24. 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

25. 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

26. Quarantines

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

28. Conclusions • 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.