Olive knot and its pathogens

Olive knot, caused by a pathogen or pathogens within the group of bacterial pathogens currently known as Pseudomonas savastanoi, is described. The ecology, transmission and methods of control of the pathogens are discussed. Strategies to minimise the effects of infection are recommended and these depend on attention to specific details in programs for pruning, irrigation and use of fertiliser. Introduction of the pathogens into previously olive knot-free countries is most likely to occur through the importation of infected nursery stock. There is no cost-effective way to control knot in olive groves by using currently available bactericidal sprays. The use of known disease-resistant cultivars and future breeding programs to improve resistance will lead to effective control in the long term. The distribution of the pathogen in Australasia is re-examined in the light of recent investigations of host specificity.