Live in NE, and about 3 weeks ago I planted cukes, zucs, yellow squash, and now I'm noticing that some of the plant stems are turning white and appear to be splitting. The plants were healthy when I transplanted, but now they appear to be stunted - not growing and fading in color.

Whatever "this" is, appears to only be effected the "vine-like" crops. Thankfully, its not bothering the tomatoes or peppers or rhubarb. Any suggestions? I'm trying to stay organic - not using pesticides. Soil is very sandy even with compost mixed in.