One of the most important activities of the Olive Oil Commission of California 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. A video of this presentation is available on the OOCC website here.
Now in its third year, the project examines how the Pseudomonas savastanoi pv. savastanoibacterium–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.
For organic operations, some formulations of copper can be applied. Although currently neither of the antibiotic treatments tested are approved for use in organic farming, Adaskaveg reports the registrant of Kasugamycin is willing to petition the National Organic Standards Board for obtaining organic status. He is hopeful it will be approved because the antibiotic is not used in humans or in animal agriculture.
Adaskaveg emphasized that the timing of application of copper bactericide is critical. Treatments done as quickly as possible, within hours following a potential infection event such as pruning or harvesting, provided the best results. He indicated that any time unexpected injuries occur such as hail, treatments should be applied preferably within 24 hours.
In 2016-17 Adaskaveg plans to continue trials with use of Deccosan 321 as an equipment sanitizer and applied directly to equipment during pruning and harvesting operations. He will also continue to test new antibiotic treatments, develop copper-activity enhancing materials, conduct field trials after rain events, and further examine the efficacy of high rates of copper mixtures to improve disease control.
Annual reports on this project are available here.