Simulated rainfall following the preplant application of 2,4-D and dicamba in soybean

ABSTRACT Soil residues following the application of 2,4-D and dicamba for weed control may delay the establishment and initial development of soybean, but rainfall can reduce the interval required between application and sowing. Rainfall volumes (0; 10; 30; 60; and 90 mm) were simulated following the application of 2,4-D (300 and 600 g a.e. ha-1) and dicamba (120 and 240 g a.e. ha-1), and the effects on soybean were evaluated. The application of 2,4-D did not affect the soybean establishment or initial development, regardless of the simulated rainfall volume. However, the dicamba residual reduced the soybean establishment for the lower rainfall volumes. Phytotoxicity was more severe for the highest dicamba rate (75-100 %), being 50-100 % for the lowest rate. The higher volumes of simulated rainfall reduced the phytotoxicity of dicamba in soybean, but were not sufficient to reduce the deleterious effects on the initial development of the crop.摘要：用于杂草防控的2,4-D和麦草畏（dicamba）施用后残留于土壤中的药剂，可能会延迟大豆的出苗定植及初期生长发育，但降雨可缩短施药与播种之间所需的间隔时长。本研究模拟了施药后不同降雨量（0、10、30、60和90 mm）的情景，分别设置2,4-D（300和600 g a.e. ha⁻¹）和麦草畏（120和240 g a.e. ha⁻¹）的施用剂量，评估了两种药剂对大豆的影响。结果显示，无论模拟降雨量如何，施用2,4-D均不会对大豆出苗定植及初期生长产生影响。然而，在低降雨量情景下，麦草畏的土壤残留会降低大豆的出苗率。麦草畏的药害程度随施用剂量升高而加重：最高剂量下药害率达75%~100%，最低剂量下药害率为50%~100%。模拟降雨量越高，麦草畏对大豆的药害程度越低，但仍不足以缓解其对大豆初期生长发育的不利影响。