Herbicidal activity of essential oils extracted from different Eucalyptus and Citrus species against Avena fatua

Weeds are a serious threat for crop yield and quality since they compete for water, light, soil nutrients and space. Avena fatua L. is one of the ten worst annual weeds of temperate agricultural regions of the world. It could reduce annual crop yields by as much as 70%. The main traits of this species include high fecundity, self-pollination, and variable degrees of primary seed dormancy. A. fatua is in the 4th position of herbicide resistant weeds in the word. It has developed resistance to eight different modes of action. .. The European legislation also supports weed control by means of Integrated Pest Management. It is important to manage A. fatua interference preventing environmental pollution and health hazards. Essential oils (EOs) are natural plant products, biodegradable, that contain natural flavors and fragrances. Some of them are classified as Generally Recognized As Safe (GRAS) for ingestion by the U.S. Food and Drug Administration’s (FDA). EOs from Eucalyptus and Citrus species had shown strong inhibitory effects on germination of seeds of many crops and weeds. Besides, each species was demonstrated to have different biological activity. The aim of this study was to verify the phytotoxic potential of the EOs extracted from different Eucalyptus and Citrus species for the management and control of A. fatua.. EOs were obtained by hydrodistillation from leaves of four Eucalyptus species (E. camaldulensis Dehnh., E. lesouefii Maiden, E. occidentalis Endl., E. torquata Luehm.) growing wild in Sicily and Tunisia and from peel fruits of three Citrus species (C. sinensis (L.) Osbeck, C. limon (L.) Osbeck, C. reticulata Blanco) from Sicily. The experiments were performed in vivo applying essential oils in postemergence, irrigated and sprayed. Soil for the experiments was collected from the topsoil (<5 cm) of a citrus field non treated with herbicides , air-dried and sieved at 1 cm. A. fatua seeds were purchased from Herbiseed (England), and germinated in a germination-growth chamber during April and May 2018, at 23.0 +/- 0.1 °C, 8 h in light and 18.0 +/- 0.1 °C, 18 h in dark. Once the seedlings of A. fatua emerged, they were placed on pots (8x8x7 cm) previously filled with 2 cm of perlite and 5 cm of soil. Ten replicates per treatment were prepared. Pots were placed in the greenhouse of the UPV. In order to find the most effective dose of EOs and its adequate mode of application, different concentrations were used: 12, 16, 20 µL/mL for Eucalyptus species and 12, 18, 24 µL/mL for Citrus species. Fitoil was used as emulsifier at a concentration of 0.05% (v/v). Plants of A. fatua, were treated at two-leaf stage, using two methods: irrigating and spraying. To monitor the experiments, photos were taken after 24, 48 and 72 hours; and then once a week. The photos were processed with Digimizer software to take different data: efficacy of the treatment, level of damage, height of plants.