One of the stars of the recent cover crop craze are forage or tillage radishes. Some people also add turnips, while others just stick with radishes. Planted early enough in the fall, they can reach a good height and produce large radish tubers.
By spring, Jenny Vogel, district conservationist with the Natural Resources Conservation Service, notes that the radishes in most seasons are dead. Only remnants remain. However, it's what they did while growing last fall that counts.
The radishes can produce tubers several inches deep. Then it's the tap root that grows off the end of the radish that can help the soil. It can grow another two feet or so, fracturing soil as it goes. The net result is that forage radishes can help make channels in the soil by rooting. They also leave organic matter behind that will decay and release nutrients during the upcoming season.
If forage radishes or turnips were the only cover crop that was planted, than natural winterkill will mean you may not need a burndown for them this spring. If you included winter oats, they were also killed off during the winter. If you mixed in annual ryegrass to have something growing this spring, then you will need to kill it off. Use the highest labeled rate and follow instructions carefully when knocking out annual ryegrass so it won't regrow and cause problems with the crop you're growing this year.
One year ago due to the mild winter some forage radishes survived into spring. Killing them is not a big issue. However, this past winter most reports say they were killed off, although many persisted well up into the winter before temperatures got cold enough to knock them out. They can tolerate more cold weather than some cover crops, like oats.Cover Crops: Best Management Practices.