Response of Soybeans to 2,4-D, Dicamba, and Picloram

Field experiments were conducted for 2 years at Urbana, Illinois, to evaluate the response of soybeans (Glycine max (L.) Merr., var. Harosoy 63) to soil and foliar applications of 3,6-dichloro-o-anisic acid (dicamba), 4-amino-3,5,6-trichloropicolinic acid (picloram), and (2,4-dichlorophenoxy)acetic acid (2,4-D). Soil incorporated applications of 2,4-D or dicamba at rates up to 8 oz/A or 4 oz/A, respectively, just before planting soybeans did not reduce soybean yields significantly. Picloram, applied under the same conditions, reduced soybean yield almost 40% at ½ oz/A. Picloram at rates from ½ to 2 oz/A caused slight to moderate leaf malformation on soybeans planted the following year but did not reduce yield. Foliar applications of 2,4-D up to 2 oz/A on soybeans had little effect on yield when applied at the prebloom stage and only slightly reduced yield when applied during flowering. Dicamba and picloram injured soybeans at the prebloom stage considerably more than did 2,4-D. Dicamba and picloram severely restricted soybean development, and reduced yield markedly when applied during flowering; ½ oz/A of dicamba or ⅛ oz/A of picloram reduced soybean yield about 50%.