Investigation of the effects of plant extracts containing allelopathic compounds as natural herbicides for controlling yellow-thorn and wild safflower in chickpea crops

The use of plant extracts containing inhibitory compounds and the evaluation of their toxic effects on weeds can contribute to reducing the reliance on chemical herbicides. This study aimed to investigate the effects of natural herbicide treatments derived from plant extracts containing allelochemical compounds as natural herbicides for controlling yellow-thorn (Picnomon acarna) and wild safflower (Carthamus oxyacantha) in chickpea (Cicer arietinum) fields during the cropping seasons of 2021-2022 and 2022-2023. In both years, the experimental treatments included ethanolic extracts of chamomile (Anthemis odontostephana Boiss.) at 50 g L⁻¹, artichoke (Gundelia tournefortii L.) at 100 g L⁻¹, and peanut (Arachis hypogaea L.) shells at 100 g L⁻¹, applied via foliar spray; pelargonic acid; the herbicide Challenge, and a control (distilled water). The results indicated that, among the applied treatments, chamomile extract (CE) presented the highest toxicity to both weed species. Compared with the control, the CE significantly reduced weed biomass by 55.53% and increased chickpea biomass by 73.81%. The combined data analysis revealed that the greatest inhibition of yellow-thorn and wild safflower growth was observed after treatment with CE in the first year, with inhibition rates of 70.47% and 82.83%, respectively. In the second year, yellow-thorn and wild safflower treated with CE presented a reduction in greenness of 55.36% and 53.44%, respectively, compared with the control in the same year, indicating the phytotoxic effect of the extract. Notably, the stomatal conductance of yellow-thorn and wild safflower treated with CE in the second year decreased by 37.40% and 37.85%, respectively, compared with that of the untreated control in the same year. The yellow-thorn plants in the pelargonic acid and control treatments in the first year presented the lowest chlorophyll fluorescence, which was 18.82% lower than that in the control in the second year. Additionally, CE treatment in the second year resulted in a 41.86% reduction in the chlorophyll fluorescence of wild safflower compared with that of the control in the first year. Gas chromatography‒mass spectrometry (GC‒MS) analysis of the volatile fraction (essential oil) of CE revealed 21 compounds, with terpenoids being the primary active components. The compounds myrtenyl acetate, decanoic acid, spathulenol, and caryophyllene oxide were the most abundant constituents of the essential oil fraction. The significant inhibitory and herbicidal activity observed in chamomile can be attributed to myrtenyl acetate. Overall, this study provides valuable insights into the substantial inhibitory effects of CE on yellow-thorn and wild safflower, which may be utilized for the development of environmentally friendly plant-based herbicides. Terpenoids, notably myrtenyl acetate (20.37%) with its herbicidal effects, along with decanoic acid (9.85%), spathulenol (7.99%), and caryophyllene oxide (5.12%), were confirmed in the volatile fraction of the CE due to their bioactive properties.