LAUSR

Olive knot, caused by the wound pathogen Pseudomonas savastanoi pv. savastanoi, is a serious bacterial disease that can be disseminated by orchard equipment. Greenhouse studies confirmed that cutting tools contaminated during contact with olive knots are able to spread the pathogen to healthy olive tissue. Quaternary ammonium compounds (QACs) were assessed as sanitizing agents for contaminated equipment as a disease management strategy. In laboratory in vitro tests, QACs exhibited high toxicity against the bacterium over a broad pH range from 6 to 9 using short exposure periods (15 to 60 s) and low concentrations (5 µg/ml). QACs applied to contaminated hard surfaces in the presence of an organic load reduced bacterial recovery by ≥3.6 log10 CFU/ml. In field trials, sanitation of hedging equipment that was contaminated with the pathogen (2 × 107 CFU/ml) and used to prune olives, was successful and sometimes completely prevented new infections from occurring. Application of additional foliar spray treatments of copper or copper-kasugamycin mixtures after hedging significantly improved disease control. In laboratory and field studies, sodium hypochlorite was significantly less effective than QAC compounds in the presence of organic matter. A nonphenolic QAC formulation, however, was ineffective as a preventative treatment when applied prior to inoculation of olive wounds, whereas a copper hydroxide application was highly effective. Based on data from this research, a QAC formulation was registered for field use as a sanitizer for olive equipment in California in 2015.