Mark VanGessel, Extension Weed Specialist; firstname.lastname@example.org
When we had similar weather a few years ago and many of the forage radishes survived, I did not have much luck killing radishes with herbicides. My concern is the likelihood of radishes re-growing if only the foliage is removed. I am thinking that we need to be sure the crown portion of the plant is also killed. With lack of experience on how to kill radishes, I don’t have any sure-fire approaches.
Some folks say that mowing will terminate these plants. We did not have a mower that would allow us get the blades low enough to remove the crown. Likewise, disking was not sufficient to kill the radishes either.
Glyphosate is not very effective on radishes. Therefore, in areas where it is appropriate, I would suggest 2,4-D (at a rate of 1 qt for 4lb/gal). It would be fine to tankmix it with glyphosate to control rye and other species.
Situations where 2,4-D is not appropriate are more challenging. Paraquat (2 qts) with a triazine herbicide (simazine, atrazine or metribuzin) would be a suggestion.
If the triazines interfere with crop rotation, then only paraquat, but a second application maybe needed.
I would suggest killing the radishes early because: 1) we don’t have a sure-fire approach and this allows time to retreat if needed; 2) allows for the root to start to break down so it won’t interfere with planting; and 3) radishes will be killed before they start to flower and produce seeds.