i dont really know but it looks like it might be some type of Crotalaria. it looks a lot like the kind i have except yours seem to be more vining whereas mine is bushier. so it may be something totally different, although there are dozens of species. i'm not sure if that would be blooming yet though. does it have seed pods that rattle ("rattlepod")?
The local name for it here is "wild peanut". It may be toxic but luckily our cattle don't mess with it. The dead tops sometimes break off and blow around like tumblweed.
We had pretty poor results using 2-4,d, last year we went to Remedy and water and that knocked it out. We spot sprayed because of the amount of clover in the field and didn;t want to get it. It's funny that we only have one field that has any of the stuff.
We live in Central Texas and we have the same weed. Our county extension agent said they have a very extensive root system. He said you can spray them, but they will come back up next year. We can not spot spray, because we have acres of them. We are going to spray this weekend to try and set them back. The county extension agent also said when you spray to mix something in it to make the weed spray really stick yo the leaves.