One of the most important activities of the Olive Oil Commission of California (OOCC)
is the funding of research projects. One such project currently in
progress examines potential treatments to prevent olive knot in
California orchards.
The work is being done by
Dr. Jim Adaskaveg, noted researcher from the Department of Plant
Pathology and Microbiology at the University of California, Riverside.
Dr. Adaskaveg gave a thorough presentation on this project as part of
the OOCC’s Informational Meeting held in January.
Now in its third year, the project examines how the Pseudomonas
savastanoi pv. savastanoi bacterium–which causes olive rot knot–
spreads, how producers can best manage the disease, and tests new
treatments for control and prevention of this disease. Olive knot is the
most destructive disease facing the olive industries in California and
can lead to defoliation, tree dieback, reduced yields, and ultimately
tree death.
Olive production has evolved into high density cultivation and
mechanization of pruning and harvesting practices. Although these
operations are highly efficient, they may create injuries to the trees.
Wounds are the primary way the bacterial pathogen enters the olive host.
Injury can also be caused by low temperatures, hail, and during normal
leaf drop these result in leaf scar which is susceptible to infection.
When an infection in an olive tree occurs, it may take several months
for the tell-tale “knot” to form on tree branches. In Adaskaveg’s work,
all knots sampled contained the bacterium and when hydrated – as might
occur from rain – the knots will begin to ooze bacterium. Therefore,
reducing the number of knots on infected olive trees, will work to
reduce the level of disease in an orchard but most importantly
prevention is the key focus to managing olive knot.
Some of the
cultural practices recommended by Adaskaveg to prevent spread of the
disease include maintaining tree vigor, reducing tree stress and
protecting leaf scars after leaf drop. It is also suggested that pruning
and removal of knots take place during dry periods and not when rain is
imminent. Adaskaveg stresses that it’s important to disinfect pruning
tools and field equipment to prevent spread of the pathogen from one
tree to the next. A new quaternary ammonium sanitizer was studied with
very good results and was registered under a Special Local Need (Section
24D) as a result of this project. This compound is already used in many
olive oil mills to sanitize equipment and a product called Deccosan 321
was registered for use on California olive groves last year.
Treatment
of olive trees with copper-based products has traditionally been used
to prevent spread of the pathogen and to protect olive trees from the
disease. Most strains of the disease are sensitive to copper, but there
is the potential for trees to build a resistance to copper after
repeated application. For this reason, the project examines new
bactericides that can help kill the pathogen before knots can form.
The
most promising bactericide products studied are antibiotics, but
because of concern about the use of antibiotics in agriculture, an
antibiotic called Kasugamycin – which is not used in animal or human
medicine – was tested in field trials. Kasugamycin is currently going
through the IR-4 Program so that it can be registered for use on
California olives. Another antibiotic, oxytetracycline, was also
recently accepted into the IR-4 program. A benefit of antibiotic
products is that they are applied well in advance of harvest and result
in zero residues present on the olives at time of harvest. Both of these
products can be used in rotation with copper to prevent the disease
from becoming resistant to any one of these products. Adaskaveg’s
research shows that orchards treated with the combination of these three
products resulted in excellent control of the disease. More
Interim Project / Research Progress Report available
here