Published May 30, 2023
BY SARA EYJOLFSDOTTIR
Millions of trees are killed every year in California by sudden Oak Death, an exotic disease severely impacting local ecosystems, which inspired the creation of the Sudden Oak Death Blitz in 2008, a yearly survey conducted by volunteers designed to track the frequency and spread of the tree disease in areas across California, hosted most recently at an event at Palo Corona on April 1.
This forest disease is caused by a non-native introduced pathogen called phytophthora ramorum, the same species of organism responsible for the Irish Potato Famine. First reported in California in the early 1990s with Big Sur being among the areas impacted initially, sudden oak death infects and kills oaks, which act as keystone species in their ecosystems. The term originates from the keystone of an arch, the irreplaceable component providing strength and stability to the rest of the structure.
“Sudden oak death is likely the worst exotic disease to have arrived in the United States in the late 20th century,” says Matteo Garbelotto, the director of the University of California Berkeley Forest Pathology and Mycology Laboratory and one of the foremost experts on the disease.
The Blitz, a citizen science project, centers on providing communities with the materials and the knowledge to identify symptoms of sudden oak death and independently sample oak trees that may be affected by the disease. These samples are sent to U.C. Berkeley to be processed, resulting in a thorough survey map from across California that is an integral aspect of disease control.
“Sudden oak death was originally spread from infected ornamental plants,” says Garbeletto, who created the first PCR test ever used officially by a government in 2004, not the intrusive COVID test, but one that analyzed a plant sample for genetic material from a virus. “These ornamentals that were being sold nationwide needed to be tested for the disease.”
The Sudden Oak Death Blitz 2022 found that 45.8% of the trees sampled in Big Sur were positive for the disease after the region of Big Sur proper was confirmed as a constant hotspot in 2020.
The disease is capable of spreading independently through wind and rain, with recent increased rainfall generating concern over a potential uptick in the spread of the disease in critical areas.
“The pathogen is very much water-loving,” explains researcher Kerri Frangioso, who has been working on sudden oak death-related projects focused mainly in Big Sur since 2000. “This year, we’re curious to see how recent rainfall will affect the pathogen and the spread of the disease.”
From the Oregon border of Del Norte County to the southernmost border of San Luis Obispo, 24 Blitzes took place in 2022, surveying roughly 10,600 trees for sudden oak death. Officially, there are about 400 collectors a year participating throughout California, and since one collector could be an individual or a family of four, there are an estimated 400 to 700 participants.
Results for the Monterey County Blitz are expected to be released in October. Sudden Oak Death Blitzes will continue across coastal California throughout the spring with open access to all.
Those interested in participating can visit www.sodblitz.org for more information.