Sudden Oak Death (SOD)

Summary of UC Berkeley 2013 Sudden Oak Death Blitz

In 2013, Matteo Garbelotto’s UC Berkeley Forest Pathology and Mycology Lab not only compiled the results from the 2013 SOD blitz, but also analyzed the last six years of SOD blitzes with an outside partner, the Ross Meentemeyer lab in North Carolina.

Research Findings

Note: While we have summarized the presentation below, the following resources are also available:

Results from SOD Blitz Data – 2006-2013 (slide 22):

Quality of Data is High: The data gathered from citizen scientists during the SOD blitzes has proven to produce very effective data. In some years the citizen scientists gathered more accurate data than the professionals. The analysis has generated an accurate risk map.

Risk and Temperature: Risk increases when monthly mean temperature between December and May is lower (cooler temperature = increased spread rate). This confirms their initial observation of a dual epidemiological pattern between the warmer interior and the cooler coastal areas

Risk and Population: Risk is lower in highly populated areas

Risk and Previous Year Infection: Risk is higher where infection the previous year was higher. The problem starts when there’s a large infestation. Multiple years of data will increase our ability to predict where the pathogen will go. The maps show how high the risk of infection is where you live

Risk and Precipitation: Risk is higher with increased precipitation and higher bay laurel density. Note that decrease is gradual during dry spells, but increase is rapid at the onset of rainfall.

VARIATION IN INFECTION RATE 2012-2013 (Slide 18):

  • With a dry 2013, overall infection rates decreased (-5%) as expected
  • Two sites had a significant increase: South Skyline and Santa Cruz.
  • A significant decrease was noticed in Napa.
  • Although the difference may be due to sampling error, it is interesting to note that increases were in two colder areas and decrease in a hotter area
  • This observation matches conclusions from last year that epidemiology of disease is different between the coastal forests and the forest that are somewhat inland

INFECTION IS DIFFERENT IN COASTAL & INLAND ZONES (See slide 19):

Truly Coastal: Mendocino, West Sonoma, Marin County, San Francisco, North Peninsula, South Skyline, Santa Cruz, Big Sur, West of the Berkeley-Oakland hills

  • Wet-dry cycles effect infection rates, but the pathogens remain high all of the time. They are in outbreak mode on a constant basis. Dry spells lower populations of the pathogen but levels remain high even during drought: much longer epidemic phase, short periods of rain (3 months) will bring the numbers up.

Somewhat Inland: Central and East Sonoma, most of Napa, East of Oakland Berkeley Hills, South peninsula

  • Dry spells lead to build up. It may take one or more years for the oaks to be at risk. During dry spells (1 year or longer), populations of the pathogen decrease significantly and disease enters chronic phase, with very limited risk of oak infection. It may take over a year for pathogen populations to climb up to the epidemic phase, in which oaks can be infected.

ELIMINATION OF CONTINUOUSLY INFECTED TREES MAY BE BENEFICIAL (See slide 20):

Trees that are continuously infected (5%), especially in dry years, are the source of infection, and their elimination may be extremely beneficial.

NORTH PENINSULA 2013 FINDINGS (See slide 39):

  • Outbreak in Burlingame Hills remains significant and probably larger than expected.
  • First report in West San Mateo County, North East of Half-Moon-Bay. Potential issue for nurseries if too close.
  • First report South of Ralston Avenue, associated with apparent oak infection.

MID PENINSULA 2013 FINDINGS (See slide 41):

  • SOD North of Woodside, both West and East of 280, but with higher frequency on the mountain slopes West of 280. Increase of frequency East of 280 may require wet years.
  • No SOD in the residential areas from Atherton to Mountain View. Eradication in Atherton appears to have been effective but will need to be monitored.
  • Los Altos Hills: not an apparent increase in infection frequency (expected finding due to dry weather in an area where arrival of SOD has been more recent), but an apparent movement Eastward.

SOD MAP MOBILE APP HELPS DETERMINE RISK (See slides 51-56):

  • Identifies infected trees in the field
  • Calculates risk of oak infection at any given site
  • Free
  • Available for iPhone and Android

TREATMENT RECOMMENDATIONS HAVE CHANGED:

  • Treatment recommendations have significantly changed and will be covered at these trainings.
  • Canopy will also issue a summary of treatment recommendations in December.