This review provides information on the biological activities of chalcones (whether natural or synthetic derivatives) on different organisms, as well as an overview of the functions and possible new applications of these plant secondary metabolites on crop protection, as eco-friendly pesticides and weed control agents. Naturally occurring chalcones have been used in traditional medicine for many years; however, recent scientific advances have shown that these molecules have a broad range of biological activities in a variety of organisms. A review on the major sources of chalcones and the main molecular events involved in the modes of action of these natural products is achieved. Chalcones are molecules with a broad spectrum of biological activities, which are of great interest in agriculture to control weeds and unwanted pests.

Citral is a monoterpene commonly found as volatile component in many different aromatic plants. Although many studies have identified the presence of citral in phytotoxic essential oils, this work determines for the first time the potential herbicidal effect of citral on weeds. The use of citral against weeds and crops resulted in the potential for the management of barnyardgrass, redroot pigweed, and ribwort. Clear morphological differences were observed between adult thale cress plants exposed to citral in two different application methods: spraying and watering. Citral-sprayed and citral-watered thale cress plants showed completely different effects after treatment, suggesting that foliar or root absorption can determine the effectiveness of this compound. This work demonstrates that citral is effective not only on seedling metabolism but also on adult plants by inhibiting growth and development altering the plant oxidative status.