Resistance of Barnyardgrass (Echinochloa crus-galli) to Butachlor in direct-seeded rice in Hue city, Vietnam
Abstract
Barnyardgrass is a significant threat to rice production, causing substantial yield losses and evolving resistance to multiple herbicides. However, the occurrence of Butachlor resistance in Central Vietnam remains poorly understood, highlighting the need for its assessment in Hue City rice fields. This study evaluated the resistance of Barnyardgrass populations to Butachlor in Kim Tra ward, Hue City (16°30′35″ N, 107°31′56″ E; elevation: 0 m) during the 2024–2025, where Barnyardgrass (Echinochloa crus-galli) had been consistently observed surviving after herbicide application. A single-factor experiment was conducted with five treatments: a control (no herbicide application), and Butachlor applications at 0.5x, 1.0x (recommended dose of 0.3 kg a.i./ha), 1.5x, and 2.0x the recommended dose. Results indicated that Barnyardgrass in this region has begun to develop resistance to Butachlor. At the recommended dose, herbicide efficacy was only 38.9% at 14 days after treatment (DAT). While the 2.0x dose achieved 100% efficacy, Barnyardgrass survived and competed with rice at the recommended dose, leading to a 2.1% yield loss compared to weed-free conditions. In contrast, untreated plots suffered a 22.2% yield reduction. These findings suggest an urgent need for revised weed management strategies in Central Vietnam to mitigate the spread of herbicide resistance.