Read a lot of comments suggesting I not waste my time or money trying to kill waterhemp escapes.  Thought I'd try it anyway.  (You know how hard-headed some of us farmers can be.) 
  Sprayed a quart of Roundup with Cadet on beans in mid-June.  Seemed to take down scattered 12 inch waterhemp but it came back after 2-3 weeks.  Some of it was significantly stunted so it wouldn't cause much concern.  But a few acres were 36 inches and still growing though it was some-what stunted and not as lush as a untreated plant.  Decided to try 12.5 ozs. of Cobra with 1 pint/acre of Crop Oil using my TurboDrop twinfan nozzles which I bought years ago for a possible rust outbreak.  Twenty gallons of water/acre @ 50-60 psi.  We caught a nice 1 inch+ cloud-burst before I decided to spray last week.  Sprayed in 85 degree weather.  Checked them today and beans were dinged (of course) but the waterhemp appears to be toasted.  Worst case scenario it comes back but my beans have 2 or 3 weeks breathing room.  Hopefully, they're DEAD. 
  Just thought some of you might appreciate the imformation.