Sudden Oak Death (SOD)

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Sudden Oak Death in Marin County. Image: [1]

Sudden Oak Death (SOD) is a tree disease caused by the plant pathogen (Phytophthora ramorum). In addition to SOD, Phytophthora ramorum also causes Ramorum Blight. Phytophthora ramorum was first documented in Central California in the mid-1990s, and has since caused severe mortality of several oak tree species and most notably tanbark oak (Notholithocarpus densiflorus). In 2014, Phytophthora ramorum was estimated to extend from Santa Barbara in California to Curry County in Oregon [1]. The disease has been found worldwide. It is speculated that the disease spread world-wide via the nursery industry. Currently, restrictions exist on the movement of nursery plants, firewood, and soil to minimize the spread of the disease.

The disease was named in the mid-1990s when oak and tanbark oak trees suddenly and simultaneously exhibited signs of distress and subsequently died [2]. The severe die-back of the species gained public and political attention, and subsequently the California Oak Mortality Task Force was formed to identify the cause of the oak deaths. Today the California Oak Mortality Task Force coordinates research, monitoring, management and education of SOD.

Phytophthora ramorum affects many plant species. Phytophthora ramorum can infect and cause mortality in the following species: coast live oak, California black oak, Shreve oak, and canyon live oak, as well as tanoak trees. Phytophthora ramorum can causes twig and foliar diseases in species such as California Bay laurel, Douglas-fir, and coast redwood. These species are often hosts of pathogen, primarily responsible for the pathogen's dispersal, but themselves do not die from the disease. Implications of SOD spread include loss of habitat, loss of food sources for wildlife, increase in exposed soils, and changes in the frequency and intensity of wildfires.

Phytophthora ramorum thrives in cool, wet climates [3]. Phytophthora ramorum is a water-borne pathogen that disperses via fog, wind, water droplets, streams and splashing.

References

  1. Citation needed
  2. Garbelotto M. and Hayden KJ. 2012. Sudden Oak Death: Interactions of the Exotic Oomycete Phytophthora ramorum with Naïve North American Hosts. Eukaryotic Cell: 11(11):1313.
  3. California Oak Mortality Task Force

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