Plant resistance inducers, also called elicitors, could be useful to reduce the use of pesticides. However, their performance in controlling diseases in the field remains unsatisfactory due to lack of specific knowledge of how they can integrate crop protection practices. In this work, we focused on apple crop and acibenzolar-S-methyl (ASM), a well-known SAR (systemic acquired resistance) inducer of numerous plant species. We provide a protocol for orchard-effective control of apple scab due to the ascomycete fungus Venturia inaequalis, by applying ASM in combination with a light integrated pest management program. Besides we pave the way for future optimization levers by demonstrating in controlled conditions (i) the high influence of apple genotypes, (ii) the ability of ASM to prime defenses in newly formed leaves, (iii) the positive effect of repeated elicitor applications, (iv) the additive effect of a thinning fruit agent.

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Phosphonate-based products have demonstrated diverse abilities to protect crops against pests, with various mode of actions proposed. In this paper, we specifically investigated the potassium phosphonate (KHP) on apple crop. Its performance to control three major apple bioagressors (Venturia inaequalis, Erwinia amylovora and Dysaphis plantaginea) was evaluated under semi-controlled conditions. The product was able to confer significant protection rates (40 to 75% for apple scab, 40% for fire blight and 30% for rosy aphid) which can be explained by its more or less efficient biocidal activity against the three pests, and by its ability to induce apple immunity (PR proteins and secondary metabolites genes). A cumulative effect of treatments as well as the systemic behavior of the product was demonstrated. Fields trials against apple scab and the postharvest disease bull’s eyes rot (Neofabraea vagabunda) were performed on different apple varieties, by applying KHP combined with light pest management programs either reducing (dessert orchards) or suppressing (cider orchards) fungicide applications. KHP was able to reduce apple scab by 70 to 90% on shoots, young and harvested fruits, and bull’s eyes rot by 70 to 90% on harvested fruits. Overall, our results indicate that KHP is useful for the protection of apple trees against its major pests by direct effect and by triggering the host defense system.

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