Investigating the resistance of barnyard grass populations to pretilachlor in direct-seed rice in the Central Region of Vietnam

Barnyard grass (Echinochloa crus-galli (L.) Beauv.) is a major weed widely distributed across the world and causes serious damage to rice production. Yield loss due to barnyard grass was estimated at about 7 to 27% in Vietnam. This study aimed to investigate the rice production, weed impacts, herbicide usage and herbicide resistance in the Central Region of Vietnam. A survey of farmers producing rice and yield loss due to weeds conducted in Central Region showed that men mainly educated at primary and secondary schools was the main labour source in rice production. The density of barnyard grass and weed index was 13.9 plants m-2 and 14.1%, respectively, in the fields that weeds had regrown after application of herbicide. Screening in the greenhouse indicated that resistance to pretilachlor was found in populations of barnyard grass in Thua Thien Hue. The field trial indicated that a concentration of pretilachlor at the recommended rate (0.3 kg a.i. ha-1) was no longer effective in controlling barnyard grass. This indicates the resistance in populations of barnyard grass in Thua Thien Hue to pretilachlor in the field. The current result is the first report of resistance of barnyard grass to chloroacetamide in Vietnam.