Abstract: Field trials were conducted in 1998 and 1999 to determine the effect of delayed burndown timings on weed control and yield of no-tillage glyphosate-resistant corn planted into soybean residue and into a wheat cover crop. Burndown treatments containing glyphosate were applied to both trials when the corn was planted (PRE), when the corn began to emerge (SPIKE), or when the corn had three visible leaves (3-LEAF). As burndown timing was delayed, velvetleaf control increased in corn planted into soybean residue. Glyphosate applied at 0.84 kg ae/ha at the SPIKE or 3-LEAF timing followed by a sequential application of glyphosate at 0.84 kg/ha controlled velvetleaf 91% and corn yields were similar to the weed-free plots. Corn yields among the burndown treatments were directly related to velvetleaf control. In the wheat cover crop trial, wheat treated at the PRE timing was completely controlled and corn yields were similar to the weed-free plots. As burndown timings were delayed, corn emergence and yields were severely reduced. Glyphosate applied at 0.84 kg/ha to 25-cm-wide strips over the corn row at planting and followed with delayed burndown timings increased corn emergence and yield.
Nomenclature: Glyphosate, N-(phosphonomethyl)glycine; corn, Zea mays L. DK 493RR; velvetleaf, Abutilon theophrasti Medicus #3 ABUTH; winter wheat, Triticum aestivum L.
Additional index words: Herbicide-tolerant crops, living mulch, residual herbicides.
Abbreviations: PRE, preemergence; SPIKE, at corn emergence; 3-LEAF, corn with three visible leaves.
