Phytophthora, the organism that causes sudden oak death, has a deadly past, affecting not just plant life but human life as well.
Phytophthora infestans, just one of about 100 identified Phytophthora species, was the culprit in the 1840s Irish Potato Famine that left an estimated 2 million Irish people dead, according to USAblight.org, a U.S. Department of Agriculture (USDA) project that studies the disease in the United States. Commonly called "late blight," Phytophthora infestans was so devastating that the 1840s outbreaks launched the science of plant pathology, according to the USDA.
But Phytophthora infestans is not a disease of the past. As recently as 2009 an epidemic broke out in the northeastern U.S., according to the USDA, which calls the disease "a major threat to food security worldwide."
Globally, crop losses caused by late blight and the cost to control it are estimated at more than $6.7 million annually, the USDA states.
This year, more than 33 counties in the U.S. reported late blight in food crops. In California's Kern County, samples of the disease were found to be resistant to a fungicide used to control Phytophthora.
In 2010, the USDA's plant inspection branch listed 33 species of Phytophthora for quarantine. Among those with the greatest potential for economic harm are Phytophthora porri, which kills leeks, onions, many ornamental plant species, and possibly carrots, and Phytophthora pinifolia, which could devastate the U.S.'s $67 billion pine products industry if it gets a toehold in the country, according to the USDA.
The effects of Phytophthora could be systemic as well. Phytophthora tentaculata, the USDA noted, "could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes." It could impact threatened or endangered species by disrupting critical habitats and could significantly impact cultural practices, home and urban gardening or ornamental plantings.
In 2012, Phytophthora tentaculata appeared in a native plant nursery in Monterey County. It was the first time it appeared in the U.S. Since then, it has shown up in native plants from nurseries used for restoration projects in multiple counties, including San Mateo and Santa Clara.
Read the cover story, "Deadly disease plagues plants high above Silicon Valley"