1Nader Soltani*, 2Allan C. Kaastra, 2Clarence J. Swanton, and 1Peter H. Sikkema
Topramezone and mesotrione are two 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibiting herbicides used for broadleaf weed control in maize (Zea mays L.). Limited research has been reported on these herbicides for the control of annual grasses. Controlled environment experiments were conducted to determine the efficacy of topramezone (12.5 g ai ha-1) and mesotrione (100 g ai ha-1) on thirteen annual grass species at two development stages (2- to 3-leaf and 5- to 6-leaf). Topramezone provided consistent control of Echinochloa crus-galli (L.) Beauv. (barnyard grass), Setaria glauca (L.) Beauv. (yellow foxtail), Setaria viridis (L.) Beauv. (green foxtail), Setaria faberi Herrm. (giant foxtail), Panicum miliaceum L. (wild-proso millet), Cenchrus longispinus (Hack.) Fern. (longspine sandbur), and Panicum capillare L. (witchgrass) at both growth stages. Mesotrione provided consistent control of Echinochloa crus-galli, Digitaria ischaemum (Schreb.) Schreb. Ex Muhl. (smooth crabgrass), Digitaria sanguinalis (L.) Scop. (large crabgrass), and Panicum miliaceum at both growth stages. Both herbicides suppressed Panicum dichotomiflorum Michx. (fall panicum), but mesotrione also suppressed Setaria glauca, Cenchrus longispinus, Panicum capillare, and Bromus tectorum L. (downy brome). Topramezone provided poor control of Bromus tectorum and Avena fatua L. (wild oat), and mesotrione provided poor control of Avena fatua, Setaria faberi, and Setaria viridis at both growth stages. Increasing the growth stage of annual grasses generally did not alter the level of control by either herbicide. However, the control level of Eragrostis cilianensis (All.) Vign. Ex Janchen (stinkgrass) decreased from control to suppression with increasing growth stage with both topramezone and mesotrione. A similar decrease in the level of control was observed with topramezone on Digitaria ischaemum. Based upon the control levels determined from this research, weed management practitioners can select the appropriate herbicide for annual grass control in individual fields.
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