The present invention relates to the agricultural use of hexanoic acid and monocarboxylic acids with similar chain structure having from 5 to 8 carbon atoms, their derivatives, their salts, and aqueous mixtures thereof containing modified hexoses and/or amines. These compounds are useful as plant growth stimulants, anti-senescents, and as resistance inducers to biotic and abiotic stresses. The invention also refers to the use of caproic (hexanoic) acid as an inhibitor of spore germination and mycelium growth of phytopathogenic fungi. The use of hexanoic acid as a fungicide in both pre- and post-harvest treatments is also suggested. The inducing activity of hexanoic acid on plant defenses against phytopathogenic fungi at non-phytotoxic concentrations has been shown.