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International audience; PEPS: Evaluation and optimization of the use of plant defense stimulators (PPS) in plant protection strategies in apple orchards Activating the plant immune system with plant resistance inducers (or PRIs) could help reducing pesticides, but their practical use still raises many questions. The objective of the PEPS project, targeting apple orchards, was to i) sort through the current supply, ii) define and apply orchard integration protocols for apple scab and post-harvest diseases, and iii) increase knowledge of these products under controlled conditions. Five selected products were evaluated in orchards within a multilocal network including an INRAE experimental unit, apple technical institutes and regional experimental stations. The results showed that it is possible to reveal significant protective effects with PRIs while reducing fungicide application. However, a regularity of effect could only be obtained with one of the PRIs and only on one of the two targets. The observed variability in efficacy showed that it is essential to continue to study the factors that may interact with the action of the products. Work under controlled conditions has made it possible to achieve progress on the characteristics of PRIs, revealing that i) their effect only persists in the organs present at the time of treatment, ii) their efficacy may be disrupted by abiotic factors, iii) few inputs interact with them and when there is interaction, it is mainly additive, iv) their application in spring and pre-harvest does not cause allergen accumulation and v) their spectrum of action extends to fireblight and rosy aphid for the most effective one. The PEPS project provided new information on the use of PRIs in orchard phytosanitary control, and now makes it possible to better define the next steps for optimization.