JOURNAL HIGHLIGHTS BY STEVE RANGER
The hunt is on for alternative weed management strategies that reduce the environmental impact while maintaining effective control. Essential oils have gained attention as natural compounds with allelopathic activity, low environmental impact and reduced toxicity, showing promising results as bioherbicides.
Studies have already demonstrated that essential oils can inhibit weed germination and early growth, although their effectiveness depends on species, phenological stage and applied concentration. Citronella and citrus essential oils, particularly orange oil, have been highlighted for their ability to significantly reduce weed germination and early growth
A study published in SCI’s Pest Management Science journal has evaluated the effects of different doses of essential oils extracted from orange (Citrus sinensis) by hydrodistillation and steam distillation, and from citronella (Cymbopogon nardus and C. winterianus), on the germination and early development of Eleusine indica, Digitaria insularis, Euphorbia heterophylla and Amaranthus hybridus, with the aim of identifying efficient weed control alternatives with reduced environmental impact.
The study was conducted at the Center for Agricultural Sciences of the Federal University of São Carlos, Araras campus, São Paulo, Brazil.
‘Our interest in this area arose from the increasing number of herbicide-resistant weed biotypes in Brazil. However, this is not a problem limited to our country; it has become a global challenge, largely driven by the repeated use of herbicides with the same mode of action, which promotes the selection of resistant populations,’ said Patricia Andrea Monquero, one of the team involved with the research. ‘In addition, the ecotoxicological impacts of herbicides have been increasingly studied and discussed by the scientific community, reflecting growing public concern about the sustainability of agricultural systems and their potential effects on the environment,’ she told C&I.
‘In this context, the search for alternative methods of weed management has become increasingly important, motivating us to investigate the potential of natural compounds. Among these, citronella essential oil, which is already well known for its insecticidal properties, showed a herbicidal effect that was particularly surprising to us, suggesting that it may have applications beyond those previously recognised, she added.
The essential oils were characterised primarily by oxygenated monoterpenes and terpene hydrocarbons, notably citronellol, citronellal, geraniol and limonene.
Citronella essential oils caused strong inhibition of germination and vigour, resulting in near-total seedling suppression from 10 ml L−1 onward, the paper found.
By contrast, orange essential oils exhibited moderate effects, with partial and dose-dependent reductions in germination and early growth, and the weed species differed in their susceptibility to the essential oils.
The combined results indicate that citronella essential oils exhibit high bioactivity and stand out as promising candidates for bioherbicide development, the paper said, whereas orange essential oils show a less intense but relevant allelopathic effect, supporting their potential use as complementary tools in sustainable weed management strategies.
‘We plan to continue this research by evaluating its effects on additional weed species and conducting ecotoxicological studies to better understand its environmental safety and potential for practical application. We are also investigating essential oils from other plant species that have shown promising results and represent exciting opportunities for future research,’ Monquero said.
Essential oils as bioherbicides: effects of orange and citronella oils on weed germination and early growth
Geovana Rocha Marzochi, Leonardo de Oliveira Semensato, Francielli Santos de Oliveira, Virginia Claudia Paulino Silva, Eliane Gomes Fabri, Evandro Henrique Schinor, Andréia Cristina Silva Hirata, Moacir Rossi Forim, Angélica Correa Kauffmann, Patricia Andrea Monquero
Pest Management Science
doi.org/10.1002/ps.71009
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