Have you considered spraying in place of mowing? I have friends that never mow their plots....just spray them.
IMO this is your best option if a bushhog is out of the question and you have access to water. You can get a sprayer that will fit the back rack of your wheeler with a spray boom on it for relatively cheap. I'd spray it now if it's waste high and burn it down hard (heavy concentrate) and then spray it again 2-3 weeks or so before you disc. If it's good and dry, for a couple weeks after you kill it, it will basically just vaporize when the disc hits it. If was planning to disc with was a 4 wheeler, I'd much rather spray it than try to disc it bushhogged.
