We have let rye go to seed before planting a soybean crop.  Will have rye coming up for about the next 2 years. Corn gets planted the year after the soybeans. The stuff that comes up in July during the soybean years does not survive, nor the stuff that comes up in June during the corn year.  We plant corn at 22,000, between the shading of the ground, lack of rain and heat in August I doubt you would have very much survive if any survive.