Soltani, N., Shropshire, C. and Sikkema, P. H. 2011. Giant ragweed (Ambrosia trifidaL.) control in corn. Can. J. Plant Sci. 91: 577-581. Twelve field trials (five with PRE and seven with POST herbicides) were conducted over a 4-yr period (2006-2009) on various Ontario farms with heavy giant ragweed infestations (22 plants m^-2) to determine the effectiveness of preemergence (PRE) and postemergence (POST) herbicides for the control of giant ragweed in corn. Atrazine, dicamba, dicamba/atrazine, isoxaflutole plus atrazine, mesotrione plus atrazine, saflufenacil, and saflufenacil/dimethenamid applied PRE provided 9-52, 60-80, 64-83, 44-77, 33-80, 36-80, and 43-63% control of giant ragweed, reduced giant ragweed density 55, 45, 59, 64, 68, 73, and 77% and reduced giant ragweed shoot dry weight 60, 89, 90, 87, 83, 81, and 78%, respectively. Atrazine, dicamba, dicamba/diflufenzopyr, dicamba/atrazine, 2,4-D/atrazine, bromoxynil plus atrazine, prosulfuron plus dicamba, primisulfuron/dicamba, mesotrione plus atrazine, topramezone plus atrazine, and bentazon/atrazine applied POST provided 46-94, 70-90, 69-84, 82-94, 56-83, 59-76, 66-84, 71-81, 49-81, 34-78, and 26-84% control of giant ragweed, reduced giant ragweed density by 65, 82, 71, 82, 76, 76, 59, 65, 59, 47, and 71% and reduced giant ragweed shoot dry weight by 97, 99, 97, 99.6, 98, 98, 95, 97, 95, 88, and 96%, respectively. Based on these results, dicamba/atrazine provided the best and most consistent control of giant ragweed in corn of the PRE and POST herbicides evaluated.