Field experiments were conducted in 2002 and 2003 to evaluate total POST weed control in corn with mixtures of mesotrione, atrazine, and the commercial mixture of nicosulfuron plus rimsulfuron plus atrazine at registered and reduced rates. Treatments were compared with nicosulfuron plus rimsulfuron plus atrazine POST, and S-metolachlor plus atrazine PRE alone and followed by (fb) nicosulfuron plus rimsulfuron plus atrazine POST. All treatments controlled common lambsquarters 8 wk after the postemergence treatments (WAPT). Common ragweed control with POST mesotrione plus nicosulfuron plus rimsulfuron plus atrazine combinations was greater than 89%. Mesotrione plus the registered rate of nicosulfuron plus rimsulfuron plus atrazine POST controlled common ragweed more effectively than the PRE treatment alone. Addition of atrazine to mesotrione improved common ragweed control by at least 38 percentage points over mesotrione alone. Nicosulfuron plus rimsulfuron plus atrazine at the registered rate and in mixtures with mesotrione controlled morningglory species (pitted and ivyleaf morningglory) 89 to 91%. Large crabgrass control varied between 2002 and 2003. In 2002, large crabgrass control was 58 to 76% with all POST treatments, but in 2003, nicosulfuron plus rimsulfuron plus atrazine POST alone controlled large crabgrass greater than 86%. Large crabgrass was more effectively controlled by treatments with S-metolachlor plus atrazine PRE than by the total POST treatments in 2002. Giant foxtail was controlled at least 97% with nicosulfuron plus rimsulfuron plus atrazine treatments. S-metolachlor plus atrazine PRE fb nicosulfuron plus rimsulfuron plus atrazine POST controlled all weed species greater than 85%. Corn yields by total POST treatment combinations of mesotrione plus either rate of nicosulfuron plus rimsulfuron plus atrazine were comparable to S-metolachlor plus atrazine PRE alone or fb nicosulfuron plus rimsulfuron plus atrazine POST.
Nomenclature: Atrazine; mesotrione; nicosulfuron; rimsulfuron; S-metolachlor; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; giant foxtail, Setaria faberi Herrm. # SETFA; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; morningglory species, Ipomoea spp. # IPOSS; pitted morningglory, Ipomoea lacunosa (L.) Roth # IPOLA; corn, Zea mays L. ‘Dekalb DKC60-09 (RR2)’, ‘Pioneer 33B51’, ‘Pioneer 33G56’.
Additional index words: Reduced herbicide rates, total postemergence, sulfonylurea herbicides, triketone herbicides.
Abbreviations: DAP, days after planting; fb, followed by; WATP, weeks after treatment with POST herbicides.