Preventative Phosphonate Treatment for Sudden Oak Death Effective
for Up to Two Years
OAKLAND, Calif., Jan. 22 (AScribe Newswire) -- Treatment with
the fungicide phosphonate was effective in stemming the spread of sudden
oak death - a tree disease that has killed thousands of oaks and tanoaks
in 14 California coastal counties - for up to 2 years, according to a
series of studies by UC Berkeley researchers published in the
January-March 2009 California Agriculture journal.
Conversely, in the studies an alternative treatment comprised
of azomite soil amendments and a lime bark wash was ineffective in
stopping the spread of sudden oak death.
The alternative treatment "is like treating pneumonia with
orange juice," says Matteo Garbelotto, UC Berkeley adjunct professor of
soil pathology, whose lab conducted the studies.
The January-March 2009 issue of the University of California's
California Agriculture journal is available online:
http://californiaagriculture.ucop.edu/0901JFM/toc.html; for a free
copy, e-mail firstname.lastname@example.org.
First discovered in Marin County in 1995, sudden oak death is
caused by the exotic water mold Phytophthora ramorum, which is carried
by more than 100 plants species; it kills tanoak trees and four types of
oaks (black canyon, coast live and Shreve's). California bay laurel
trees are a major transmission source of P. ramorum in forests that they
share with oaks and tanoaks.
The UC Berkeley researchers conducted three studies: a direct
comparison of the two treatments (phosphonate and azomite soil
amendment/lime bark wash) on potted oak trees in greenhouses; a field
study that measured the efficacy of treatments 6, 12 and 18 months
afterward; and a treatment efficacy study using potted plants that had
been "wounded" and artificially infected with P. ramorum. In the field
study, the authors developed a new method in which branches of infected
trees were brought back to the laboratory, so that living trees would
not be placed at risk.
"Our [studies] indicated that phosphonate treatments had a
significant effect at 6,12 and 18 months post-application," wrote
Garbelotto and co-author Doug Schmidt of UC Berkeley. "Because most P.
ramorum infections occur in late winter and spring, 18 months of
coverage will adequately protect trees for 2 years."
Phosphonate is the only legally registered treatment for
sudden oak death in California. It is recommended to prevent the disease
in areas where P. ramorum has been found, but it does not cure trees
that have already been infected. The azomite soil amendment/lime bark
wash treatment is not registered, but has been marketed as a natural way
to bolster tree defenses against sudden oak death.
"Azomite appeals emotionally to a lot of people," says Janice
Alexander of the California Oak Mortality Task Force. "Now we'll be able
to tell them that it doesn't work."
The phosphonate treatment is considered environmentally
friendly. It is applied either by drilling holes in trees and injecting
the fungicide into the tree cambium, or topically to tree bark in
mixture with a surfactant called Pentrabark.
Garbelotto and his colleagues have been offering sudden oak
death treatment workshops for professional tree-care specialists and
"We advise treating oaks with no sign of infection when
symptoms show up on neighboring bay laurels," Garbelotto says. "We also
advise that even if some oaks have died in a grove, it may be possible
to protect those that have not been infected."
Etiology and Evidence of Systemic
Acidification In SOD Affected Forests In California
Data on pH from 34,700 soil samples taken from a wide range of
agricultural and forest soils in California indicate that between 14
and 21% of the soils are acidic (pH < 6.0) and 3 to 4% are strongly
acidic (pH < 5.0). However, a subset of samples taken from
SOD-affected sites indicates that 72% of these soils are acidic and
4% are strongly acidic (median pH = 5.7; n = 132). The soils from
these sites were also found to be consistently low in Ca and very
high in soluble Al and Fe. Spatial analysis reveals a strong coastal
gradient in soil pH with the lowest pH values found near the coast.
Strong coastal gradients are also
apparent in soil Ca, which is
lowest near the coast, and in soil Al, which is highest near the
coast. Precipitation chemistry data from this region also reveal a
coastal pH gradient much like that found in the soils. Similar
coastal gradients in precipitation pH have been reported from the
Olympic peninsula, from southeast Alaska, and from Scandinavia.
These results lend further support to the theory that systemic
acidification is adversely affecting the
health of the trees and
soils in SOD-affected forests. The situation described here in
California is not unlike that in other regions of the world where
aging forests are experiencing decline. From this and other work
(e.g., studies at Hubbard Brook), we strongly believe that the cause
(and the definition) of SOD is still an open question, and that the
scope of SOD research should be expanded to include studies of
by cryptogams in the context of forest and soil