Abstract: A device for protecting crop plants (P) and/or sown seeds (S) against unwanted plants is provided to avoid the use of chemical weed control agents or herbicides. The device includes a ribbon or lace-shaped structure on which a plurality of annular elements are arranged at a distance from one another, in which the structure is designed to be applied to a cultivated surface (F) such that each element encloses the location (O) of a crop plant (P) or sown seed (S), and wherein each element includes a detectable means for marking the location concerned (O1, O2, . . . On) for detection by a machine for controlling mechanical weed control mechanisms. The device is thus an auxiliary or marking means which can be easily applied on the cultivated surface along the row of plants or seeds and allows reliable detection by machine of the locations of plants or seeds, zones to be protected.