Roundup kills most weeds, but not all. Without knowing what you have in your fields, that's hard to answer. If you can, add some 2,4,d. Do you plan on disking? If so, that will bring up dormant weed seed that will sprout with a vengeance next spring. IF your looking for a really clean field come spring, then wait a couple weeks after you disk and spray anything that is coming up, and then plant, without rediscing. The problem with starting this late in the year, is that some weeds and grasses are starting to go dormant and may not resprout, in a few weeks. I would try and plant some annual clovers in the lower ph plots and try to get those up to mid 6 range. I know this is a lot of trouble, but a little hard work now will pay off big time come spring. I don't disc anymore so I don't have to worry about that part of it. I use the throw and mow method, really saves a lot of time. In mid April, if grasses start to show up, hit them early with clethodim before the grass goes to seed.