Potential natural herbicide found in Mexican marigold essential oil

The Mexican marigold (Tagetes erecta) was evaluated by a Thai study that sought out a natural and effective replacement for synthetic herbicides. The essential oils found in the plant demonstrated sufficient effectiveness against cockspur grass (Echinochloa cruss-galli) before and after the emergence of the weed.

King Mongkut’s Institute of Technology supported this research effort. The findings came out in the journal Industrial Crops and Products.

• The essential oil was extracted from Mexican marigold samples. After undergoing analysis to determine its specific chemical composition, it was turned into emulsifiable concentrate and tested as a herbicide.
• The concentrate was sprayed on the ground that contained cockspur grass seeds that had not yet emerged from the soil. A dose of 2 milliliters per liter was determined to be the minimum concentration that completely stopped the germination and growth of the weed’s seeds. The essential oil stopped the activity of alpha-amylase that is vital to healthy growth.
• The emulsifiable concentrate was also tested in the post-emergence phase of the weed. Different doses were applied to cockspur grass 21 days after the pest plant emerged from the ground.
• Post-emergence weeds treated with the concentrate exhibited wilt and desiccation. The phytotoxic effects grew more severe with increasing concentrations. The cockspur grass showed much lower levels of chlorophyll and carotenoids, suggesting that the essential oil targets photosynthesis.
• Furthermore, the emulsifiable concentrate undermined the membrane of the cockspur grass, making it more vulnerable to injury and infection. The essential oil also increased the substances that reacted to thiobarbituric acid.

The researchers concluded that the essential oil of Mexican marigold is a potential herbicide whose phytotoxic activity can naturally manage weeds by disrupting photosynthetic metabolism.

Journal Reference:

Laosinwattana C, Wichittrakarn P, Teerarak M. CHEMICAL COMPOSITION AND HERBICIDAL ACTION OF ESSENTIAL OIL FROM TAGETES ERECTA L. LEAVES. Industrial Crops and Products. 2018;126:129–134. DOI: 10.1016/j.indcrop.2018.10.013