Efficacy of systemic acquired resistance inducers in olive leaf spot management

Olive leaf spot caused by Spilocaea oleagina is mainly controlled by copper fungicides but there is a growing need for alternative control strategies, such as induced resistance. This study investigated the potential for control of the disease with products reported to induce systemic acquired resistance. The eight products: salicylic acid (SA), 5-chlorosalicylic acid, chitosan, brotomax, 3-amino butyric acid, Foli-R-Fos 400, acibenzolar-S-methyl, potassium silicate and copper sulphate fungicide were used as foliar spray applications, and potassium silicate also as a soil drench. All compounds except brotomax, 5-chlorosalicylic acid and potassium silicate (foliar spray) reduced disease severity, by 48-89 %, with salicylic acid being most effective. SA reduced disease severity by 89 and 87 % when applied 2 or 4 weeks prior to inoculation, respectively, which was similar to the standard copper sulphate spray. In general, the inducers were more effective in reducing disease severity when plants were treated twice than when treated once prior to inoculation. The level of disease reduction was similar for all treatments (68-86 %) when applied 4+2 weeks prior to pathogen inoculation, except for brotomax (52 %). This investigation has identified products that may be used in organic or integrated management programmes for control of olive leaf spot, thereby reducing potential harmful effects such as fungicide resistance and accumulation of copper in orchard soils.