Point Reyes Light - August 3, 2000
New oak fungus blamed for West Marin oak deaths
The discovery of a fungus similar to the one that caused the Irish potato famine was announced this week as a breakthrough in the search for causes of the Sudden Oak Death syndrome afflicting West Marin's coast live oaks and tanoaks.
The oak dieoff has been widespread from Big Sur to Mendocino County and has decimated stands in parts of Marin County. The tell-tale brown leaves are readily apparent to anyone surveying the hillside while driving along Nicasio Valley Road, on Sir Francis Drake Boulevard over White's Hill, or all along Lucas Valley Road.
The fungus now believed responsible for the dieoff was identified by Paul Rizzo, a UC Davis plant pathologist who has been investigating Sudden Oak Death Syndrome with a team of state researchers. The fungus infects oak trees through their bark and produces enzymes that cause oozing sores on the tree as its bark cells are broken down.
Tires & pets Because the fungus spores can travel in infected wood or soil, Rizzo warned that it might also be spread inland from the coast on people's shoes, animal's feet, or car and bicycle tires.
"Preventing the movement of soil and wood will be critical to slowing the spread of the fungus to other oak woodlands, such as the Sierra Nevada," he said. "In particular, firewood and soil should not be moved from coastal areas."
The discovery led county supervisors this week to consider whether they may impose a quarantine on infected wood to keep the fungus from spreading.
However, deputy agricultural commissioner Fred Crowler said Wednesday that it is too soon to take such a step. To declare a quarantine, he said, the fungus must be proven as the primary agent causing Sudden Oak Death syndrome.
Oaks infected with the fungus also become highly vulnerable to the oak bark and ambrosia beetles, which bore into the tree and contribute to the tree's quick demise.
Origins unknown Crowler said a quarantine must limit the disease to a defined area, but it is not even known where the outbreak now ranges. Rizzo said it is uncertain whether the fungus was brought to California or is a native species that has recently evolved into a tree-killer.
The fungus does not match any of the 60 known species of the genus Phytophtora, an airborne variety of which causes potato blight. The microscopic spores like cool, wet conditions typical to coastal forests and use a pair of tails called flagella to swim easily through water.
This feature of the fungus leads Crowler to suspect that the series of unusually wet winters on the coast may have contributed to its rapid spread. However, he said, that is only one more bit of speculation about why the coast's signature oaks have started dying.
For now, Crowler said, people with infected trees should follow the suggested procedure of cutting them down immediately and encasing the wood in plastic for six months to kill off all the beetles inside. He also urged people not to move infected wood from their property as a precaution against spreading the fungus.
Okay as mulch Crowler was uncertain whether chipping the wood would spread fungus spores but reasoned that using the chips as mulch would kill off the pathogens.
Homeowners should also take precautions not to place their oaks under undue stress by overwatering or disturbing their roots. Dead or drying branches may be pruned at anytime, but additional pruning should be avoided during the growing season, according to the UC Cooperative Extension.