Field experiments were conducted to evaluate the influence of three nitrogen fertilizer application timings on corn and giant ragweed dry weight, corn and giant ragweed nitrogen accumulation, and corn grain yield. By the V8 growth stage, corn plants in treatments which included nitrogen at planting accumulated up to 27% more dry weight and 26% more leaf area than corn in sidedress-only treatments that had not yet received any fertilizer nitrogen. Nitrogen fertilizer application timing did not influence early-season giant ragweed dry weight, but did influence N accumulation. Giant ragweed at 0.5 plants/m² accumulated up to 16 kg N/ha in 40-cm-tall plants by the V8 corn growth stage and up to 104 kg N/ha when allowed to remain in corn until the end of the growing season. At this density of giant ragweed, corn yields were not reduced if removed by the V8 corn growth stage. However, season-long interference reduced corn yields by up to 19% regardless of nitrogen application timing. Early-season giant ragweed growth was less responsive to nitrogen application timing than corn, suggesting that nitrogen management programs should not be altered significantly to influence giant ragweed competitiveness in corn. However, giant ragweed should be removed in a timely manner to minimize nitrogen accumulation in nitrogen-limiting corn production situations.

Nomenclature: Giant ragweed, Ambrosia trifida L. AMBTR, corn, Zea mays L. ‘DKC60-09RR2/YGCB’ and ‘DKC61-45RR/YGCB’