The invention defines a composition for agricultural use comprising an active ingredient consisting of a quebracho extract, a mimosa extract or a combination thereof. Likewise, the invention defines a method for preparing said composition and a method for applying same. This composition is effective against oomycetes and fungi in plants fit to be cultivated, its mechanism of action being indirect since the treated plants develop a mechanism complementing the resistance to said pathogens, so it can also be used in a preventive manner. The composition of the invention is also effective for controlling or preventing problems caused by abiotic stress in plants (water stress, cold weather, hot weather, etc.), while at the same time successfully increasing plant vigor and health.
