Differential sensitivity of Echinochloa muricata and Echinochloa crus‐galli to 4‐hydroxyphenyl pyruvate dioxygenase‐ and acetolactate synthase‐inhibiting herbicides in maize

De Cauwer B, Rombaut R, Bulcke R & Reheul D (2012). Differential sensitivity of Echinochloa muricata and Echinochloa crus‐galli to 4‐hydroxyphenyl pyruvate dioxygenase‐ and acetolactate synthase‐inhibiting herbicides in maize. Weed Research52, 500–509. Summary Echinochloa muricata var. microstachya (rough barnyard grass), an alien species native to North America, has gradually spread and is now locally naturalised and abundant in and around maize fields in Flanders (Belgium). One of the possible reasons for its expansion in maize fields might be a lower sensitivity to post‐emergence herbicides acting against panicoid grasses, in particular those inhibiting 4‐hydroxyphenyl pyruvate dioxygenase (HPPD) and acetolactate synthase (ALS). Dose–response pot experiments were conducted in the glasshouse to evaluate the effectiveness of four foliar‐applied HPPD‐inhibiting herbicides (sulcotrione, mesotrione, topramezone and tembotrione) and the ALS‐inhibiting herbicide nicosulphuron for controlling Belgian populations of Echinochloa crus‐galli (barnyard grass) and E. muricata. Herbicides were applied at the four‐leaf stage (BBCH stage 14). Pre‐emergence bioassays were included to evaluate soil activity of the HPPD inhibitors topramezone, sulcotrione and mesotrione. In another dose–response pot experiment, the influence of growth stage at time of herbicide application on efficacy of topramezone for Echinochloa control was evaluated. Sensitivity to HPPD inhibitors topramezone and sulcotrione was significantly lower for E. muricata populations than for E. crus‐galli populations. However, no differential sensitivity to nicosulfuron and the triketones tembotrione and mesotrione was found. Compared with E. crus‐galli, satisfactory post‐emergence control of E. muricata required 5‐ to 14‐fold higher doses of topramezone and sulcotrione, as well as a more timely application. Compared with E. crus‐galli, sensitivity of E. muricata to topramezone was more dependent on growth stage. Owing to the intragenus variability in sensitivity to HPPD‐inhibitor herbicides, higher awareness of the presence of E. muricata plants in maize fields is required.