Weed Control with Starch-Encapsulated Alachlor, Metolachlor, and Atrazine

Field research was conducted at Rosemount, MN in 1990 and 1991 to determine the effect of starch encapsulation on weed control in corn with alachlor, metolachlor, and atrazine under two weed densities. At low weed densities (122 total plants/m2), giant foxtail and Pennsylvania smartweed control were not different with full rates of herbicide applied in starch encapsulated or commercial formulations. Velvetleaf control was less with starch-encapsulated than commercial formulations regardless of velvetleaf density. At high giant foxtail densities (740 plants/m2), control was not affected by formulation with full rates of alachlor plus atrazine. However, giant foxtail control was less with starch-encapsulated formulations than commercial formulations with 75% rates of alachlor plus atrazine and both 75 and 100% rates of metolachlor plus atrazine. At low weed densities, corn yield was not different with any treatment, except starch-encapsulated metolachlor plus atrazine at 75% rates, compared to the weed-free control. Alachlor plus atrazine at full rates was the only starch-encapsulated treatment to result in corn yield not different from the weed-free control at high weed densities. Conversely, all commercial formulation treatments resulted in corn yields not different from the weed-free control at high weed densities.