– Mark VanGessel, Extension Weed Specialist; mjv@udel.edu
When we had weather similar to this winter’s a few years ago and many of the forage radishes survived, I did not have much luck with killing radishes with herbicides. My concern is the likelihood of radishes regrowing 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. So in areas where it is appropriate to use 2,4-D that is the product I would suggest (at a rate of 1 qt for 4lb/gal). Tankmixing 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.
However, farmers should also walk their fields and see how many radishes are really alive, there may not be as many as they think. In addition, if they planted mixed species, they need to weigh the pros and cons of terminating the field. Terminating the radishes will also kill other species.