Inadequate corn stands due to extreme weather conditions may require producers to replant their corn fields. The use of GR corn, however, can result in difficulty in managing replanted corn without experiencing yield loss. Therefore, the objectives of this research were to evaluate the herbicide options for control of GR corn in a corn replant situation and to determine the effect of corn replanted into various initial corn stands on grain yield. Two field studies were conducted to accomplish the objectives. The first experiment was designed to identify the most efficacious herbicide treatment for GR corn removal in a corn replant situation. Clethodim (51 g ai ha−1) applied 6 d prior to replanting, paraquat (700 g ai ha−1) plus metribuzin (160 g ai ha−1) applied at replanting, and glufosinate (450 g ai ha−1) applied at replanting along with a sequential treatment 3 wk later provided 96 to 100% control of the initial corn stand and resulted in the highest yield. If corn from the first planting remains, the interaction between different sized plants can reduce yield of corn. Thus, a second field experiment was conducted to evaluate the influence on grain yield of corn replanted into various initial corn stands. Corn stands of 0, 20,000, 40,000, 60,000, 80,000, and 100,000 plants ha−1 were established and either followed by a corn replant at 80,000 seeds ha−1 or not replanted. Initial stands ≥ 60,000 plants ha−1 did not require a replant to maximize yield. Initial corn stands ≤ 40,000 plants ha−1 required a replant with initial stand control to maximize grain yield. The percent yield contribution from an initial stand of 20,000 plants ha−1 was 20% greater than the same population replanted a few weeks later, which showed the competitive advantage to earlier planting even at the lowest initial corn stand. Because of this competitive advantage, an initial stand must be removed to maximize corn yield in a replant situation.

Field research was conducted to determine the effectiveness of glyphosate, fomesafen, and adjuvant combinations on 6‐inch glyphosate‐resistant (GR) and 12‐inch glyphosate‐sensitive (GS) giant ragweed. Glyphosate alone controlled GS giant ragweed greater than 93%, but control of GR giant ragweed was less than 47%. GS and GR giant ragweed responded similarly to fomesafen as control ranged from 42 to 86%. Control with reduced rates of fomesafen was enhanced with additional adjuvants. Regardless of adjuvant, the labeled use rate of fomesafen alone at 0.352 lb/acre provided 75 to 86% control of both GR and GS giant ragweed. The addition of glyphosate to fomesafen resulted in over 90% control of GS giant ragweed. The addition of glyphosate to fomesafen did not improve control of GR giant ragweed and when additional adjuvants were not used, control was reduced when glyphosate was added to 0.352 lb/acre of fomesafen.