Q: Can I use a herbicide like Callisto, with mesotrione as its active ingredient, now and plant radishes and turnips for a cover crop in early September?

A: There is no mention of turnip or radish on the Callisto label. That means the industry never tested those species for planting interval or the restriction is too long to allow for planting of that forage cover crop species within the same growing season as corn. If you plan to plant a cover crop to provide soil health benefits and NOT to be used as animal feed, you can plant any cover crop species, assuming the potential risk of any residual herbicide damage to the cover crop.

The Nebraska Extension NebGuide, Herbicide Options for Planting Forage Cover Crops Following Corn and Soybean (G2276), would be useful reading to understand the difference between cover crops and forage crops and how the intended use affects the selection of herbicide.