I think there were more weeds, but different kinds 60-70 yrs ago. Our main nemesis was Giant Foxtail in this area. It was hard to cover in the row with a cultivator and 2,4-d was only for b-leaves. Weeds used to be so bad in some places that you might have to wait for a killing frost to combine beans. Or, risk slugging the little cylinders and spending hours trying to clean them out. Corn pickers would have the snapping rolls wind up with GFT and you had the same thing. Sometimes breaking the slip clutches after they got tired of slipping. 

Then weed seed would be bad enough that  you might get docked on it. It was embarrassing at the elevator watching that green pile of GFT seeds block the pit grates. 

Then there were clean years also. Not always a nightmare. We cultivated corn 2x, and beans mostly 3x. Then there was one other operation in the beans....walking. 

But, the weeds were different as others say. We fought GFT, lambsquarter, smart weeds, cockleburr, and velvetleaf, which we called buttonweeds. Then there was AMG (morningglories) also. They would wind up in both the combine reels and the snapping rolls. Most all of them meant you had to alter your harvest plans to suit the weed. Wait for the dew to dry or wait for a killing frost. We don't do either of them much any more.

We had one of the early self propelled combines (Oliver 30) and often turned down custom combine requests based on what we saw from the road. It was different then. I remember we had to go to a field day a relative few years ago to view this new weed that would be causing trouble in the midwest......known as waterhemp. That was a new one to us. Not any more though.