Breakthrough for Treatment of Oak Death
Scientists say Product Helps Infected trees fight disease

Peter Fimrite, San Francisco Chronicle Staff Writer (sfgate.com)

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 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

©2003 San Francisco Chronicle

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