The control of glyphosate-resistant corn in corn replant situations and the effect of nitrogen timing on volunteer corn interference in hybrid corn (2011)

Rapid adoption of glyphosate-resistant (GR) corn hybrids has led to the reemergence of volunteer corn as a problematic weed in soybean and corn and has made controlling the initial stand of corn in a replant situation more difficult. Clethodim and glufosinate are often used to control GR corn in corn replant situations and in soybean. The objectives of this research were to evaluate the response of two hybrid corn varieties and their F2 progeny to clethodim and glufosinate and to evaluate the effect of plant nitrogen (N) concentration on clethodim and glufosinate efficacy. DeKalb 63-42 was more tolerant to clethodim than 60-18 and 60-18F2. No differences were found between the hybrids and their respective F2 progeny in the response to clethodim or glufosinate. In a second dose-response study assessing the effect of N conditions on herbicide efficacy, both clethodim and glufosinate were less injurious to plants growing in low N than in high N availability. Earlier corn planting dates results in difficult to control GR corn in a replant situation with herbicides labeled for use in corn. In addition, little is known about the effect that a partial initial corn stand has on replanted corn yields. 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 replanted corn into various initial corn stands on grain yield. Clethodim (51 g ai ha−1) applied 6 days 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 weeks later provided 96 to 100% control of the initial corn stands and resulted in the highest yield. A second field experiment was conducted to evaluate the influence on grain yield of replanted corn into various initial corn stands. Initial corn stands ≤ 40,000 plants ha−1, required a replant with initial stand control to maximize grain yield, while initial stands ≥ 60,000 plants ha−1 did not require a replant to maximize yield. The percent yield contribution from an initial stand of 20,000 plants ha−1 was 20% greater than the replant stand indicating a competitive advantage even at the lowest initial corn stand. Due to this competitive advantage an initial stand must be removed to maximize corn yield in a replant situation. Volunteer corn (VC) may interfere with hybrid corn for nitrogen (N), reducing grain yield and the interference may be influenced by N management. Field experiments were established to determine the effects that N fertilizer management and VC interference have on hybrid corn growth and grain yield. Treatments consisted of three VC densities, a control (0 plants m−2 ), a low density (1 plant m−2), a high density (4 plants m−2), and six N fertilizer treatments (0 kg N ha−1, 67 kg N ha−1 at planting, 67 kg N ha−1 at planting + 133 kg N ha−1 at V5 corn growth stage, 67 kg N ha−1 at planting +133 kg N ha−1 at V10 corn growth stage, 200 kg N ha −1 at V5 corn growth stage, and 200 kg N ha−1 at V10 corn growth stage). When 200 kg N ha−1 was applied, regardless of application timing, hybrid corn dry weight, hybrid corn N accumulation, and hybrid corn grain yield were reduced by the high VC density. However, when VC grain yield was added to hybrid corn grain yield VC density did not affect total grain yield. When 0 and 67 kg N ha−1 were applied, neither hybrid dry weight or hybrid N accumulation were affected by either VC density, but hybrid corn grain yield and total grain yield were both reduced by the high VC density. N fertilizer application timing had no effect on hybrid corn dry weight, N accumulation, or grain yield. Late N fertilizer applications (200 kg N ha−1 at V10 and 67 kg N ha −1 at planting +133 kg N ha−1 at V10) resulted in greater VC N accumulation, VC grain yield, and total yield. However, the potential problems associated with VC should result in management practices to reduce the presence of VC in corn.