Organomineral Fertilizer Mitigates Phytotoxicity of PPO-Inhibiting Herbicides in Direct-Seeded Onion

Onion (Allium cepa L.) is highly sensitive to post-emergence herbicides, which limits chemical weed management, particularly under direct-seeding systems. In this context, organomineral fertilizers with biostimulant properties may represent a promising strategy to mitigate herbicide-induced phytotoxicity. This study evaluated the potential of an organomineral fertilizer to reduce phytotoxicity caused by post-emergence PPO-inhibiting herbicides in direct-seeded onion. A field experiment was conducted using a randomized complete block design with four replications. Treatments consisted of sequential applications of oxyfluorfen, flumioxazin, and oxyfluorfen + flumioxazin, combined with organomineral fertilizer application either as a tank mix or 3 days after herbicide application (DAA). Oxyfluorfen showed the highest crop selectivity, with phytotoxicity remaining below 15% throughout the experimental period, whereas the oxyfluorfen + flumioxazin combination caused the greatest injury, reaching 35% at 7 days after the first application. Treatments containing flumioxazin resulted in greater reductions in photosynthetic pigments and bulb yield. The organomineral fertilizer reduced phytotoxicity to as low as 5% in flumioxazin-treated plants and increased total bulb yield by 21.46% when applied as a tank mix and by 16.18% when applied at 3 DAA. These results indicate that organomineral fertilizer application can reduce visible injury and increase bulb yield under PPO-inhibiting herbicide treatments in direct-seeded onion.