Originally I thought you had a mustard - but I agree with you assessment of wild radish -

I've got it in my corn this year too - it is real tough - I can't mow - and I'll have a million seeds next year.

Here's a link

http://www.ppws.vt.edu/scott/weed_id/rapra.htm

You can see it in this picture of my corn plot from June - It got worse!



Mow is you can - its tough to get rid of - I'll be planting a round up ready plot the next 2 years on this field to try to reduce the residual seed base.