Dose-response of Bergamot Juice as a Post-emergence Bioherbicide on Young and Established Weed Regrowth Under Field Conditions in South-western Cote d'Ivoire

The search for effective and environmentally sustainable bioherbicides is a key objective in integrated weed management. This study evaluated the herbicidal potential of bergamot (<i>Citrus bergamia</i>) juice, a by-product of the essential oil industry, based on its high acetic acid content. Field experiments were conducted using a randomized complete block design to test five application rates (1,500, 1,200, 900, 600, and 300 L ha<sup>-1</sup>) on two contrasting weed communities: young regrowth (one week after mowing) and established weeds (four months after mowing). Efficacy was assessed over 60 days using the Henderson-Tilton formula and the European Weed Research Council (EWRC) rating scale. Soil pH was analyzed post-trial to detect acidification. <i>A central finding was the stark contrast in efficacy based on weed growth stage.</i> On established weeds, the rates of 1,500 L ha<sup>-1</sup> and 900 L ha<sup>-1</sup> provided the best control, with a residual activity of 30-45 days and efficacy >90% for up to 45 Days After Application (DAA). <i>In sharp contrast, the treatment was largely ineffective on young regrowth,</i> with even the highest doses providing only transient control that declined to very poor efficacy (≤31%) by 60 DAA. Results demonstrated that bergamot juice provided effective control of a broad spectrum of broadleaf weeds, including <i>Phyllanthus amarus</i> and <i>Ageratum conyzoides</i>, but showed poor efficacy against several grass species, particularly <i>Paspalum dilatatum</i>. Critically, no significant or consistent changes in soil pH were detected following application. The findings confirm that bergamot juice is a viable contact bioherbicide for managing <i>established</i> broadleaf weeds without impacting soil acidity but<i> is not suitable for controlling young regrowth.</i> Further research is needed to optimize application strategies, determine its economic feasibility, and fully elucidate its efficacy spectrum for commercial adoption.