Berkeley professor finds possible treatment for ‘Sudden Oak Death’

In an experiment on 90 potted oaks, forest pathologist Matteo Garbelotto used chemical treatments to slow the effects of "Sudden Oak Death."

14 March 2001 | Chemical treatments tested on 90 potted oaks infected with the so-called “Sudden Oak Death,” may stave off the deadly disease, Matteo Garbelotto, a Berkeley forest pathologist, reported at a March 9 community meeting in Marin County.

In an experiment conducted between August and March, three chemical treatments were effective in significantly slowing down the formation of lesions caused by the pathogen, said the adjunct professor in the Department of Environmental. Science, Policy & Management. The finding raises the possibility of treating individual trees in a landscape setting, but the problem at the ecosystem level remains.

“This is quite striking,” said Garbelotto. “I didn’t expect to get this type of response.”

Previously, no treatments have been available for the disease. The deadly microbe — caused by a brown algae belonging to the genus phytophthora — has spread quickly in oak trees from Sonoma County to Monterey County, killing hundreds of thousands of tan oaks, coast live oaks and black oaks. It also has been found in huckleberry bushes in Marin County and in commercial rhododendron plants at nurseries in Germany, the Netherlands and Santa Cruz County.

The disease is related to the species that caused the 1845 potato famine in Ireland, researchers reported, but unlike the other 60 species of phytophthora, this variety attacks both the leaves, stems and, perhaps, roots of oaks.

Researchers are concerned that the disease could spread around the world if not contained. Oregon has put California oak products under a 90-day quarantine, and hikers and bikers are being asked to clean their boots and tires to prevent the spread of the disease. A $10.3 million bill to combat the disease is currently pending in the California legislature and $3.5 million in federal money has been approved for research leading to a cure.

In his experiments, Garbelotto infected potted trees with phytophthora in August and November and then, within 60-70 hours of the second application, treated all of them with one of four chemical compounds: copper sulfate, al-fosetyl, metalaxyl or phosphonate. The diseased oaks were either injected with the chemical, had their soil drenched with the chemical compound or were treated topically.

Injections of phosphonate worked best, he said, reducing fungal growth by as much as three to four times the rate at which it spread and significantly reducing lesions.

Preliminary results showed that al-fosetyl and metalaxyl proved somewhat effective, but the pathogen could become resistant to it, Garbelotto said. Copper sulfate did not work, but if used to coat the tree, it could prevent phytophthora from entering the oak.

More tests must be done to confirm the treatment. If phosphonate proves to be the magic bullet, homeowners and nursery owners may finally have a line of defense against the disease. However, forestry officials and researchers will have to find a way to apply it easily and safely to open space and national forests in the seven affected counties.