My area isn't nearly as big, but what I did was cover it with some tarps for a few weeks. Killed everything. Then I tilled it up very shallowly and sprinkled the seeds. Worked great.The area I am looking to seed is better described as a field. It's about 200ftx100ft. The old lady would kill me if I covered the place with round-up, especially considering we live close to a reservoir. I am thinking of renting a roto-tiller.
My other issue begins with when we bought the house about a year ago. It was owned by the HUD and there was a disclaimer stating that there were "wetland issues." After some research I learned that one of the neighbors had notified the conservation commision about the previous owners plans to build something in the backyard. The previous owner ended up having to pay some scientist to come here and make sure he had not done any damage to the so called "wetlands" (there is a very small brook running through this portion of the land, along with some patchy wet spots but I would not call it wetlands by any means." Anyways, I do not want any nosy neighbors calling the con-com on me if I go an till up everything.
Well, I am kind of late in the game now, so I have until next spring to come up with a plan.