Allelopathic effect of maize residue on the growth of sunflower weeds

Sunflower productivity in Iraq is hindered by weed competition, necessitating effective yet sustainable control methods. Integrating maize residues with herbicide applications may enhance weed suppression while improving soil properties. This study investigates the effect of incorporating maize residues and Metricam herbicide on weed growth in sunflower fields during 2024 at the University of Baghdad. Maize residues and Metricam herbicide were applied to the field soil at 50% and 75% of the recommended dose, individually and in combination. Additionally, two treatments were included: a full recommended herbicide dose and a weed-free control for comparative analysis. Maize residues and Metricam herbicide significantly reduced weed density and dry weight in sunflower fields, with the greatest suppression observed when combined. The 50% herbicide dose with Baghdad3 and Al-Maha residues achieved superior control (86 and 75%; 85 and 76%) compared to the full recommended dose (71 and 63%). The 75% herbicide dose with residues showed the highest inhibition (76% for Baghdad3, 69% for Al-Maha), outperforming the full-dose herbicide alone (45% for Al-Maha). Soil phenolic content peaked at two to four weeks post-application, coinciding with reduced weed germination. Applying 75% of the recommended Metricam dose with maize residues effectively suppressed weed growth in sunflower fields.