Sudden Oak Death

Phytophthora ramorum (Pr) is a pathogen new to science that causes 3 distinctly different diseases- ramorum leaf blight, ramorum shoot dieback, and a killing stem canker disease of oak and tanoak better known as sudden oak death. It is a fungus-like organism not native to North America and many species and cultivars of popular woody landscape plants are counted among the hosts. Pr poses an international risk to vulnerable oak and tanoak ecosystems via accidental introduction on infected nursery stock.

Background

• Pr was found in the mid-1990's in European ornamental nurseries on Rhododendron and Viburnum and simultaneously in central coastal CA killing coast live and CA black oaks.
  
• The first Pr-infected ornamental nursery stock in CA was detected in 2001, and APHIS promulgated rules governing interstate commerce in host species in 2002. International quarantines have been put in place by the EU, Canada, South Korea, and Australia.
  
• The US nursery industry was not heavily impacted until 2003 when infected stock was found in CA, OR, and WA.
  
• The host range has since grown to 42 genera of nursery and forest plants representing all forest strata from the herbaceous understory to woody canopy species.
  
• The geographic range in North American forest landscapes is currently limited to 14 central coastal CA counties and one county in southwest OR. However, 1.5 million potentially infected nursery host plants were accidentally shipped to all 50 states from a southern CA nursery in 2003-04 and again in separate incidents in 2004-05.

Project Highlights

• FHM-Research synthesized known pathogen epidemiology (hosts, environment, and introduction pathways) into a national risk map that guides early detection surveys.
  
• National survey protocols are written and training conducted by R8-FHP. State forestry agency cooperators conduct the field surveys and submit plant samples to molecular diagnostic labs in state universities.
  
• A pilot survey to develop methods in 7 high-risk eastern states in woody ornamental nursery perimeters and general forest areas was funded by FHM in '03. 172 locations were surveyed; 1,116 symptomatic host samples were negative for Pr. (Accidental introduction was occurring at the time, but this fact was not known until March of '04.)
  
• The discovery of accidental introduction resulted in the expansion of the survey to 36 states in '04. Cumulative results to date are: 1,119 locations surveyed; 5,633 samples processed; 2 positive for Pr, both from San Francisco Co. CA (surrounded by known positive counties).
  
• The survey will be expanded to 38 states in '05. Total funding = $0.4 million in '03; $1.3 million each in '04 and '05 for a total of $3.0 million over 3 years, all through FHM.
  
• Pr has been confirmed in nursery stock in 20 states (a few in landscapes in GA and SC), but is not known to occur in forest ecosystems outside the infested west coast counties.

Challenges

• Highest risk areas are in the forest interface in urban and wildland settings where infected ornamentals have been planted and remain undetected. The Cooperative Extension Service has the mandate here, but may not be adequately trained or funded to attack the problem.
  
• Cost sharing requirements for our state cooperators sometimes impede survey logistics.
  
• Continued interagency cooperation with APHIS, state departments of agriculture, state forestry agencies, FHM, and FHP.
  
• Research needs in epidemiology, particularly as concerns eastern species and early detection methods (e.g. stream water sampling and baiting for Pr).

Conclusions/Future direction

• Based on past history, it is not a matter of "if", but "when" Pr will gain a foothold in eastern oak forests. Due to a lack of basic epidemiological research on eastern species, the range of outcomes is extremely uncertain- from innocuous to a potential chestnut blight scenario.
  
• FHP continues to cooperate with APHIS and state partners in the development of early detection, delimitation, containment, and eradication strategies. Containment and eradication protocols for forest ecosystems are in APHIS review at this time.

More Information

Animal and Plant Health Inspection Service

California Oak Mortality Task Force

USDA Forest Service, Northeastern Area

FHP Contact:

Steve Oak
USDA Forest Service
Southern Region FHP
200 Weaver BLVD
Asheville, NC 28804
Phone: (828) 257-4322
Email: soak@fs.fed.us

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USDA Forest Service - Forest Health Protection, Southern Region
Last Modified: Monday, 14 January 2013 at 09:40:58 EST