Look up a picture of rapeseed. A lot of vegetables/crops bloom with yellow flowers, but rapeseed fields will be overwhelmingly bursting with yellow compared to other crops.
I really read your question wrong
I thought you wanted to know if it was weed, not a weed. I think weed flowers but I don't think they are yellow. Not that I have experience with that, of course
I know my cousin hasn't been able to plant his crops yet either. He said any longer and they loose the whole season. On top of that, to prevent flooding along the Mississippi, many of the fields have been flooded to save neighborhoods. I expect the fall harvest to very minimal, and prices to stay high with the lack of crops.
I'm from Indiana and all of the fields around us have tall yellow flowers in them. They are weeds. We call them golden rods (or as ds4 says hot rods). I'm unsure if that is their actual name or a slang name.