Economic Threshold of Volunteer Corn GR® in Soybean as a Function of Emergence Time and Origin of Corn

ABSTRACT: Volunteer corn is extremely competitive with soybean and the degree of interference varies with the corn density, time of emergence and origin. The objectives of this work were to determine the economic threshold (ET) of volunteer corn GR® F2 in soybean as a function of the time of emergence (same day and nine days after soybean) and origin (individual plants or clumps). Each clump was manually adjusted to have seven corn plants. Four field experiments were conducted in randomized blocks design with four replicates in Passo Fundo, RS, Brazil. The soybean yield losses (%) were calculated and adjusted to the model of the rectangular hyperbola and generated the parameters for the determination of the ET, that was calculated based on the volunteer corn control costs (US$ ha-1), efficiency of control (%), price paid for soybean (US$ kg-1) and soybean yield (kg ha-1). The ET mean was 0.3 and 0.48 for individual corn plants m-2 emerged together and nine days after soybean, and 0.08 and 0.03 m-2 for individual plants and clumps, respectively. Increases in grain yield and price paid for soybean, greater control efficiency of corn and lower control cost promote reduction in the ET of volunteer corn in soybean. The control of volunteer corn is justified in a density less than 0.5 individual plant m-2 and is close to zero when corn originates from clumps. Volunteer corn is one of the most competitive weed in soybean crops.

摘要：自生玉米（volunteer corn）与大豆的竞争关系极强，其干扰程度随玉米种植密度、出苗时间及起源类型的不同而存在差异。本研究旨在明确大豆田GR® F2代自生玉米的经济阈值（economic threshold，ET），并分析该阈值与出苗时间（与大豆同期出苗、大豆出苗后9 d出苗）及起源类型（单株或簇生）的关联。试验中每个簇生玉米群均经人工调整至包含7株玉米。试验于巴西南里奥格兰德州帕苏丰杜（Passo Fundo, RS, Brazil）开展，采用随机区组设计，设置4次重复，共开展4个田间试验。研究人员计算了大豆产量损失率（%），并将损失率拟合至矩形双曲线模型，得到用于确定经济阈值的相关参数；经济阈值的计算基于自生玉米防治成本（美元·公顷⁻¹）、防治效率（%）、大豆收购价（美元·千克⁻¹）及大豆实际产量（千克·公顷⁻¹）。结果表明，与大豆同期出苗的单株自生玉米、大豆出苗后9 d出苗的单株自生玉米对应的经济阈值均值分别为0.3株·米⁻²和0.48株·米⁻²；单株起源与簇生起源的自生玉米对应的经济阈值则分别为0.08株·米⁻²和0.03株·米⁻²。大豆籽粒产量与收购价提升、玉米防治效率提高及防治成本降低，均可降低大豆田自生玉米的经济阈值。当自生玉米密度低于0.5株·米⁻²时，开展防治是合理的；若自生玉米起源为簇生，则防治阈值趋近于零。自生玉米是大豆种植田中竞争力最强的杂草之一。