Glyphosate-resistant corn was no-till planted into alfalfa that was in the early bud stage (UNCUT) or had been cut 3 to 4 d earlier and baled for hay (CUT). Alfalfa control and corn yield were measured in nontreated plots as well as plots treated with glyphosate alone or tank-mixed with 2,4-D or dicamba applied at planting (AP) or POST. Alfalfa control was greater for all AP treatments of UNCUT compared to CUT alfalfa. Glyphosate plus dicamba applied AP controlled alfalfa better than the other AP treatments resulting in increased corn yield compared with other AP treatments. Postemergence applications of glyphosate alone or tank-mixed with 2,4-D or dicamba controlled alfalfa better 6 weeks after treatment than AP applications of the same herbicides; however, corn yield for AP treatments were similar or greater than the yield of POST applications of the same herbicides. Corn yield averaged 13% higher following herbicide applications to UNCUT compared with CUT alfalfa, so the value of alfalfa hay must be weighed against the loss of corn yield when making decisions concerning the management of an alfalfa–corn rotation.
Nomenclature: 2,4-D dimethylamine salt; dicamba; glyphosate; alfalfa, Medicago sativa L. #3 MEDSA; corn, Zea mays L. # ZEAMX.
Additional index words: Perennial weed control.
Abbreviations: WAT, weeks after treatment.
