The potential use of steam distillation residues from medicinal plant material as a natural agricultural agent

Medicinal plants harbour broad spectra of valuable bioactive substances that protect plants against biotic and abiotic stress and consequently are beneficial for plant health. The production of essential oils, traditionally via steam distillation, mainly yields single-digit to double-digit percentage oil contents from the dry plant material, while huge amounts of by-products of this process are not considered for further use. Giving these by-products such as the aqueous phase, the so-called hydrolate and the distilled biomass a further benefit might increase the economic value of the plant resource and its processing. This chapter aims to provide a summary of potential applications to these waste-streams, particularly potential uses of the hydrolates in pest management, as plant fortifiers and natural (‘bio’) alternatives to synthetic chemical pesticides. This is also consistent with socio-political pressures to develop a bioeconomy based on multiple, sustainable uses of resources, especially raw agricultural materials.

Giving aromatic and medicinal plants an added value beyond that of the essential oils that can be extracted from them, might not only enhance the distillation economy, but also the cultivation of these plants. This would support higher levels of biodiversity and healthier cultivation of crops in general. Thus, further investigation of the protective effects and potential applications of other components of the distillates may also promote a sustainable, bio-based agriculture.