Herbicidal Activity of Thymbra capitata (L.) Cav. Essential Oil

Abstract

The bioherbicidal potential of Thymbra capitata (L.) Cav. essential oil (EO) and its main compound carvacrol was investigated. In in vitro assays, the EO blocked the germination and seedling growth of Erigeron canadensis L., Sonchus oleraceus (L.) L., and Chenopodium album L. at 0.125 µL/mL, of Setaria verticillata (L.) P.Beauv., Avena fatua L., and Solanum nigrum L. at 0.5 µL/mL, of Amaranthus retroflexus L. at 1 µL/mL and of Portulaca oleracea L., and Echinochloa crus-galli (L.) P.Beauv. at 2 µL/mL. Under greenhouse conditions, T. capitata EO was tested towards the emergent weeds from a soil seedbank in pre and post emergence, showing strong herbicidal potential in both assays at 4 µL/mL. In addition, T. capitata EO, applied by spraying, was tested against P. oleracea, A. fatua and E. crus-galli. The species showed different sensibility to the EO, being E. crus-galli the most resistant. Experiments were performed against A. fatua testing T. capitata EO and carvacrol applied by spraying or by irrigation. It was verified that the EO was more active at the same doses in monocotyledons applied by irrigation and in dicotyledons applied by spraying. Carvacrol effects on Arabidopsis root morphology were also studied.

Potential Effects of Essential Oils Extracted from Mediterranean Aromatic Plants on Target Weeds and Soil Microorganisms

“…Regarding the latter issue, it is important to highlight that tested EOs could be an important and sustainable tool for weed management, not only by killing target weeds but also reducing their ability to compete with the crops, as they were capable to reduce their vigor and growth. Many in vitro studies have shown that T. capitata EO was able to inhibit seed germination of several noxious weeds [ 15 , 35 , 36 , 62 , 63 ], such as Erigeron bonariensis , one of the most important cosmopolite weeds especially in no-tilled soils with problems of resistance to glyphosate [ 15 , 35 , 46 ]. In addition, T. capitata has been described as an allelopathic species capable of reducing both germination and growth of neighboring species [ 64 ].…”

“…A. fatua seeds were germinated using 8 h (23.0 ± 0.1 °C)/16 h (18.0 ± 0.1 °C) light/dark conditions. Germination conditions were established based in previous works [ 36 ]. After germination (about 1 week), emerged seedlings were selected for uniformity in growth and individually transplanted in polypropylene square pots (8 × 8 × 7 cm) previously filled with a 2 cm drainage layer of perlite and a 5 cm layer of soil (220 g) collected in an organic citrus orchard (39°37′24.8″ N, 0°17′25.6″ W, Puzol, Valencia, Spain).…”

“…Due to the presence of polyphenols, T. capitata EO is used in food preservation [ 31 ] and it has been demonstrated that it possesses antioxidant properties [ 32 ]. Moreover, the antimicrobial [ 33 , 34 ] and herbicidal activities [ 15 , 35 , 36 ] of T. capitata EO have been verified. Santolina chamaecyparissus L. (cotton lavender) is an aromatic plant belonging to Asteraceae family.…”

Phytotoxic Effects and Mechanism of Action of Essential Oils and Terpenoids

“…T. capita was the most effective EO, killing all weeds at the highest dose applied (12 µL/mL), except P. oleracea , which was eliminated in 90%. As T. capitata EO demonstrated the highest herbicidal potential, it was studied more in detail, through in vitro and in vivo experiments carried out on many weeds [ 72 ] ( Table 1 ). In vitro experiments showed the strong herbicidal potential of T. capitata EO, which controlled completely the germination of different common and problematic weed species, although they showed different sensitivity to the EO, as it blocked the germination and seedling development of E. canadensis , Sonchus oleraceus (L.) L. and C. album at 0.125 μL/mL (more sensitive species), of Setaria verticillata (L.) P.…”

“…With the objective to determine which mode of application was more effective, spraying or watering, T. capitata EO was applied on A. fatua by spraying and by irrigation. Comparing the data obtained in A. fatua and in other species, it was concluded that T. capitata EO was more effective at the same doses applied by irrigation in monocotyledons and by spraying in dicotyledons [ 72 ].…”