Herbicidal activity of essential oils extracted from different Mediterranean species against Echinochloa crus galli

Weed infestation in agricultural fields can cause huge economic losses and low-quality crop yields. Echinochloa crus-galli (L.) P.Beauv. (barnyardgrass) is one of the greatest yields limiting weeds in rice cultivation systems. It is a cosmopolitan weed in both temperate and tropical regions and is reported as a weed in 36 different crops in 61 countries. The success of this weed may be attributed to the production of large numbers of small, easily dispersed seeds per plant, possession of seed dormancy, rapid development and ability to flower under a wide range of photoperiods, and relative resistance of mature plants to herbicide sprays. Thus, the best way to control barnyardgrass in an environmentally acceptable and sustainable approach is to develop eco-friendly and effective alternative means based on natural allelochemicals. Among the natural plant products, essential oils (EOs) constitute an important group. EOs may help reducing the use of synthetic herbicides and lead to less pollution and more safe agricultural products. Recently, the interest in exploring EOs with phytotoxic effects from aromatic plants for weed control has increased tremendously, because they do not persist in soil and do not leach into ground water. EOs extracted from Thymbra capitata (L.) Cav.; Mentha x piperita L.; and Santolina chamaecyparissus L. were reported to reduce the emergence and seedling growth of many weeds. The present investigation allows for a more detailed insight into the herbicidal activity of the previously mentioned EOs during spray foliar and irrigation application in post-emergence on E. crus-galli plants. T. capitata M. piperita and S. chamaecyparissus EOs were purchased from “Bordas Chinchurreta”, “Sigma-Aldrich” and and “Aromas de Ademuz”, respectively. Soil for the experiments was collected from the topsoil of a citrus field not treated with herbicides (Valencia, Spain), that was air-dried and sieved at 1 cm. E.crus-galli seeds were purchased from Herbiseed (England), and germinated in a germination-growth chamber at 30 ± 0.1 °C, 16 h in light and 20 ± 0.1 °C, 8 h in dark. Once the seedlings of E.crus-galli emerged, they were placed on pots (8x8x7 cm) filled with 2 cm of perlite at the bottom and 5 cm of the collected soil. Ten pots per treatment were prepared and placed in the greenhouse. In order to find the most effective dose of EOs and its adequate mode of application, different concentrations were used: 12, 16 and 20 µL/mL for Mentha and Santolina EOs and 4, 8 and 12 µL/mL for Thymbra EO. Fitoil was used as emulsifier at a concentration of 0.05% (v/v). Plants of barnyardgrass were treated at two-leaf stage by irrigating and spraying mode of application. 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 obtain different data: efficacy of the treatment, level of damage, height of plants, weed plant fresh and dry weight

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