Elexa is a plant booster that elicits specific defense responses in various plants against certain fungal and bacterial diseases. Rather than killing hostile fungi that attack plants, Elexa acts as a preventative and stimulative agent to protect plants from pathogens. Elexa contains 4% chitosan. In the present study, a 0.1% concentration of Elexa was used to evaluate the biological efficiency in cucumber (Cucumis sativus L.), tomato (Lycopersicum esculentum Mill.) and potato (Solanum tuberosum L.) plants, as foliar spray against fungal (Botrytis cinerea Pers., gray mold), (Pseudoperanospora cubensis (Berk & Curt) Rostow, downy mildew), (Phytophtora infestans (Mont) de Bary, late blight) and bacterial (Pseudomonas lachrymans (Smith & Ryan) Carsner, angular leaf spot) diseases in greenhouse conditions. Elexa was also used to evaluate the inhibitory effect of in vitro germination against B. cinerea Pets. and P. lachrymans (Smith & Ryan) Carsner.