|
| Deadly oak disease plagues researchers By Greg Thomas [ greg@hmbreview.com ] Published/Last Modified on Wednesday, November 19, 2008 4:52 PM PST Sudden oak death has afflicted California forests since its emergence at the turn of the century. The disease was first discovered to be affecting oak trees in Marin and Santa Cruz in the late 1990s and has since spread throughout the state, infecting an estimated 1 to 3 million trees, mainly in the central interior. Researchers aren’t sure precisely where the disease originated or how exactly it found its way to the West Coast. They predict it came from Asia on the leaves of plants via the nursery trade. Since its introduction to California it has been discovered to thrive on the leaves of bay laurels and spread to surrounding oaks and tanoaks, slowly infecting and eventually killing the trees. Now, after three years of research, a partnership between Midpeninsula Regional Open Space District and scientists from Phytosphere Research and University of California, Davis, is poised to prevent the infection from spreading any further. “At this stage of the game we have some ideas of how we can manage the disease,” said Ted Swiecki, a scientist at Phytosphere Research. “Now we’re in the process of testing the disease strategies in areas where there’s an opportunity to intervene — where the disease hasn’t affected very many trees yet or where we expect it to move into the area.” Researchers are currently testing two different methods of prevention — chemical injections and bay tree removal — in open space areas near Cupertino, Palo Alto and La Honda. “There’s been a lot of impact (in those areas) fairly recently,” Swiecki said. “We’re mainly targeting the areas where we can remove small bays to protect big oaks.” Infectious spores propagate on the leaves of bay trees and tend to spread to oaks within an 8- to 16-foot radius. However, the potential exists, in high wind conditions, for spores to corrupt oaks as far as two miles away, according to Matteo Garbelotto, UC Berkeley forest pathology and mycology extension specialist. Once an oak is infected, it begins to dry out from the top down. Its green hue turns brown and it can die within a year. The disease isn’t contagious among oaks alone — bay trees act as the “Typhoid Mary” in oak forests, Swiecki said — though it can spread among tanoaks even in the absence of bay tress. That’s the case at El Corte de Madera Open Space Preserve in La Honda, where 150 tanoaks are slated for treatment in December. There may, however, be a solution on the horizon for tanoaks. Garbelotto, over the course of his research, has discovered a handful of tanoaks unaffected by the disease. Acorns from those trees were collected and are undergoing studies at University of California, Berkeley. “The idea is that if we can find trees that are genetically resistant we can use those to replant areas that have been decimated by sudden oak death,” said Leigh Ann Maze, Midpeninsula Open Space spokeswoman. As for the oaks, “the question is, if we apply (chemical treatments) over landscape-size chunks of land, how well do they work and do they justify the cause of doing it?” Swiecki said. “That’s where we’re at now.” |