I have very successfully controlled excess vegetative growth in many crops, including soybeans, using foliar sprays of boron. Boron will shorten internodes, it knocks the sugars & excess nitrates out of the leaves for a period of time. Once this excess energy is mobile in the phloem, it moves to roots, pods/fruits, nodes & forming buds. With a crop like soybeans, it will take multiple applications. I have tried many different types & manufacturers of boron, I find the Boron Plus from Delta Ag is the most active, works the best & is not very expensive (about .32 / ounce). I suggest on soybeans rates of 8-12 oz. / acre. Add some every time you go to the field to spray a foliar. It works great for me on a wide variety of crops & I have never seen any negative effects! Good Luck!