Larry Englander, URI associate professor of plant pathology, is an expert on the closest known relative of the killer fungus. So he was asked by the U.S. Department of Agriculture and the U.S. Forest Service to quickly determine the parameters to its growth and survivability.
Sudden oak death is a water mold fungus that is causing an oozing canker on the trunk of oak trees from Big Sur, Calif. to the Oregon border. Trees infected with the fungus typically die within two or three months. Discovered in 1995 but only identified last year, the fungus has killed more than 100,000 trees and baffled scientists trying to understand it.
"It’s so brand new that virtually nothing is known about it," said Englander. "It’s still a mystery as to how it got to California. I think it needs to be in a moist environment, and this area of coastal California is like a rainforest -- very lush growth, hilly, with fog banks and rain a good part of the winter."
While the fungus has already had a devastating effect on the oak forests of California, there is an even greater concern that it could find its way across the country and wipe out the eastern forests. Scientists have tested several species of eastern oaks to see if they are susceptible to the fungus, and many are, especially red oaks.
"The fungus can definitely move from plant to plant, but that would likely restrict it to the west. Or it could be self-limiting and not move beyond its current range," explained Englander. "The big concern, though, is that people could transport it long distances either by moving plants around or by tracking infected mud from one place to another."
Sudden oak death has recently been found on a variety of ornamental shrubs, like rhododendrons and viburnums, in California nurseries that had infected oaks on the premises. While it doesn’t kill these plants, they could provide the pathway for the fungus to reach the East.
"Oaks don’t move around much, but people move ornamentals all around the country, with plants sometimes making two or three stops during the production process," Englander said. "The threat is that this California problem will soon become a nationwide problem if we don’t learn how it moves and where it can and cannot relocate successfully."
Englander notes that nurseries can control the sudden oak death pathogen with the use of a common fungicide. But if an infected plant finds its way to oak forests in the East, it could easily spread to nearby trees and become a lethal pathogen. "You can’t use fungicides to treat entire forests," he said. "That’s an overwhelming impossibility."
Rather than shut down movement of plant material to and from florists, nurseries and other plant-related industries, the USDA is supporting research to understand the biology and provide rapid detection of the pathogen so intelligent decisions can be made. That’s why Englander has been called on to find some of the answers. With a $200,000 grant from the USDA Foreign Disease-Weed Science Research Unit, he’s trying to figure out "what makes it tick and what makes it croak." By evaluating the temperature, light and moisture conditions that it needs to grow, he hopes to determine the geographic and climatic limitations on its potential expansion.
He has already found that its growth does not appear to be affected by low temperatures. "It was a surprise to me that it was able to grow at really cold temperatures – down to four degrees Celsius," Englander said. "If it’s not very sensitive to cold, then our New England winters may not be the limiting factor I had hoped."
Englander expects to identify additional growth and reproductive parameters during the next year.