Rapid adoption of glyphosate-resistant (GR) corn hybrids has led to the reemergence of volunteer corn as a problematic weed in soybean and has made controlling the initial stand of corn in a replant situation more difficult. If volunteer corn in soybean or the initial corn stand in a replant situation is not controlled, yield loss can occur. 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. First, a dose-response study was conducted with clethodim and glufosinate on DeKalb 60-18 and 60-18F2, and DeKalb 63-42 and 63-42F2 to compare the response of the hybrids and their F2 progeny to the herbicides. 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.

Volunteer corn (VC) in hybrid corn has become more prevalent in recent years and can reduce grain yield. Nitrogen (N) management can influence VC interference in corn. Field experiments were established to determine the effects of N fertilizer management and VC interference on hybrid corn growth and grain yield. Treatments consisted of three VC densities (control, 0 plants m−2; low density, 1 plant m−2; 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). The effect of VC on hybrid corn was dependent on N rate. When 200 kg N ha−1 was applied, regardless of application timing, hybrid corn dry weight, hybrid corn N content, 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 corn dry weight nor hybrid corn N content was affected by either VC density, but the high VC density reduced hybrid corn grain yield for both N rates by 19% and total grain yield by 9 and 10%, respectively. Application timing of N fertilizer had no effect on hybrid corn dry weight, N content, or grain yield. However, 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 content, VC grain yield, and total yield. Assuming the harvestability of VC, the ability of a late N treatment (V10) to maximize total grain yield allows growers to use a late N application to reduce the competitive effects of VC in hybrid corn.