Field experiments were conducted in 2001, 2002, and 2003 to evaluate PRE applications of mesotrione at 150, 230, and 310 g ai/ha alone, and in mixtures with S-metolachlor at 1,070 g ai/ha and atrazine at 560 and 1,120 g ai/ha in corn. Corn injury was 11 to 18% with all treatments in 2002 when 3.2 cm of rainfall occurred within 10 d after PRE applications, but no injury was observed in 2001 and 2003 when rainfall was 0 and 1.1 cm within 10 d after PRE applications, respectively. Rainfall following PRE herbicide applications also influenced weed control, where weed control was generally poor with all herbicide treatments in 2001. Mesotrione at 150 g/ha controlled common lambsquarters and smooth pigweed at least 95% in 2002 and 2003, but control was 70% or less in 2001. PRE mesotrione at rates of 230 or 310 g/ha controlled common ragweed at least 83% in 2002 and 2003, but control exceeded 88% with mixtures of mesotrione at rates greater than 150 g/ha plus S-metolachlor plus atrazine at 560 g/ha. Morningglory species (ivyleaf morningglory, pitted morningglory, and tall morningglory) were not consistently controlled by mesotrione alone. In 2002 and 2003, mixtures of all mesotrione rates plus S-metolachlor plus atrazine at 1,120 g/ha controlled morningglory species at least 90%. Corn treated with mesotrione at any rate plus S-metolachlor plus atrazine at 1,120 g/ha consistently produced high yields. It is concluded that control with this three-way mixture would be most consistent with a minimum rate of mesotrione at 230 g/ha and atrazine at 1,120 g/ha.

Nomenclature: Atrazine; mesotrione; S-metolachlor; common lambsquarters, Chenopodium album L. CHEAL; common ragweed, Ambrosia artemisiifolia L. AMBEL; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. IPOHE; morningglory species, Ipomoea spp. IPOSS; pitted morningglory, Ipomoea lacunosa L. IPOLA; smooth pigweed, Amaranthus hybridus L. AMACH; tall morningglory, Ipomoea purpurea (L.) Roth PHBPU; corn, Zea mays L. ‘Dekalb DKC64-10 (RR2)’, ‘Pioneer 33B51’, ‘Pioneer 33G26’.