Lately, a common question has been raised - Is it too late to spray a fall-applied residual herbicide ahead of soybeans (or corn for that matter)? The answer is that now is still a PERFECT TIME to spray, if you can. The ideal soil temperatures to spray fall residuals are below 50 F and anything above frozen. Colder soil temperatures like these minimize fall breakdown of the residual product and maximize spring residual. The issue really comes to how late you are able to run a liquid floater in the cold weather.
By the way, dandelions and fall mustards (and a few tougher perennials) are still green and sending nutrition downward to roots, so spraying glyphosate or a phenoxy with the residual is not entirely out of the question if these weeds are present. We will not see a lot (if any) fall foliar burn on the weeds anymore, but the results next spring will be noticeable, because we moved the products to the plant roots this fall.