From the San Francisco Chronicle

By Peter Fimrite

Breakthrough for treatment of oak death
Scientists say product helps infected trees fight disease

Friday, October 3, 2003

The first major breakthrough in the treatment of the tree killer known as sudden oak death has been approved for use on oaks, a development that could save thousands of homeowners' trees from the plague.

The phosphite product, developed by the Australian company AGRICHEM, protects endangered oaks from infection and helps infected trees fight off the disease, according to UC scientists.

The California Department of Pesticide Regulation approved two versions of the compound Wednesday -- one is a spray, the other an injection -- for use by professional arborists and foresters.

"This is not the final solution," warned Matteo Garbelotto, the UC Berkeley forest pathologist who has led scientific research on the deadly microbe. "It is just one tool in a series of efforts to stop the spread of the pathogen. But it also gives us hope. The general belief had always been that you can't do anything to stop disease in the forest. This shows there are things that can be done."

The microscopic disease, known scientifically as Phytophthora ramorum, has killed tens of thousands of tan oak, coast live oak and black oak trees in California and Oregon, and has spread to at least 27 other tree and shrub species, most of which act as hosts but do not die.

Scientists believe 11 other kinds of plants and trees have also been infected, but the research verifying them as carriers has not been completed.

The virulent microbe, which throws off spores like flowers shed pollen, has, in essence, scraped whole sections of California's oak dotted hills and valleys bare.

In some canyons in Big Sur every tan oak tree has been killed. Some 40 to 45 percent of the majestic live oaks have died in hard-hit areas, including Marin County.

The chemical, also known as phosphonate, is expected to be available for use on private trees by Oct. 22, after arborists who want to use the product go through two days of training at UC Berkeley.

On Thursday, Garbelotto demonstrated its use -- expected to cost homeowners about $30 per tree for the material plus the cost labor for an average application*. One way to treat oaks is to inject the chemical into the tree's vascular system with a syringe. The other is to spray the bark with a mixture of phosphite and organosilicate, a chemical that helps the bark absorb the chemicals.

Phosphite is absorbed into the tree and moves up into the leaves, Garbelotto said. It then enters the cambium, the part of the tree the pathogen attacks. The presence of phosphites in the cambium prompts the tree to release chemicals that fight off infections, he said.

The original studies on phosphonate in 2001 showed marked reductions in lesions on trees, but it was registered as a fertilizer and could not be used to fight sudden oak death.

Garbelotto said further studies in Australia, where a different phytophthora is killing trees, proved the compound worked against the kind of disease affecting oaks.

The new product is good news for homeowners whose oak trees can add $30,000 to the value of their property.

But the battle continues on many other fronts.

The disease has been found in nursery plants in Sacramento and in Placer and Stanislaus counties; in King County, Washington; and in Medford and Portland, Ore. A nursery in Vancouver, B.C., was also found to have the disease.

And, for the first time, the two mating types of the disease were recently found in Portland, leading to fears that the two could mate and create a new kind of killer immune to the phosphite treatment. The other mating type was previously found only in Europe.

And, even if the disease can be controlled in some places by the newly approved chemicals, it can still live for years and years in hosts like the bay tree and infect future generations of oak trees.

* Highlighted language not in original article as published.  Prices are set by individual services providers not UC Berkeley.