I have planted a few organic soybeans in my kitchen garden. They had been doing very well but after this latest rain several of the plants have developed very pronounced brownish (color of chewing tobacco) discoloring along the veins of some of their leaves. It is only along part of the leaf but it causes the stem to wilt. Any idea what it is and/or what can be done about it? I am using a straw bale planting method. Please be advised that I am trying to keep my garden as organic as possible. Thanks!