An integrated approach to control glyphosate-resistant Ambrosia trifida with tillage and herbicides in glyphosate-resistant maize

Glyphosate-resistant Ambrosia trifida is a competitive and difficult-to-control annual broad-leaved weed in several agronomic crops in the Midwestern United States and Ontario, Canada. The objectives of this study were to compare treatments for control of glyphosate-resistant A. trifida with tillage followed by pre-emergence (PRE) and/or post-emergence (POST) herbicides in glyphosate-resistant maize and to determine the impact of A. trifida escapes on maize yield. Field experiments were conducted in 2013 and 2014 in grower fields infested with glyphosate-resistant A. trifida. Tillage prior to maize sowing resulted in 80-85% control compared with no tillage. Tillage followed by PRE application of saflufenacil plus dimethenamid-P with or without atrazine resulted in 99% control compared with <= 86 and 96% control with PRE herbicides alone at 7 and 21 days after application respectively. Tillage or POST-only herbicides resulted in 4-14 A. trifida plants m(-2), whereas a PRE and POST programme had <3 plants m(-2). Maize yield was greatest (13.1-14.2 tonnes ha(-1)) with tillage followed by PRE and POST herbicide programme. The relationship between maize yield and late-season density of A. trifida escapes showed a 50% maize yield reduction irrespective of control measures when A. trifida density was 8.4 plants m(-2). It was concluded that the combination of tillage with PRE and/or POST herbicides reduced A. trifida density and biomass accumulation early in the season and provided an integrated approach for effective management.