In a recent post, Purdue University researchers posted an article on the use of herbicides on cover crops. Herbicide manufacturers don’t address cover crops, per se, so Purdue is offering some new insights.
Here’s a portion of the article. Click here to see the entire article, which includes a chart with different cover crops and herbicides used for burndown.
One question that has been brought up in recent cover crop situations is replant timing when cover crops are planted after the use of residual herbicides used in corn or soybean. There are several plant species being promoted for the use of cover crops. Some of the plants include annual ryegrass, wheat, buckwheat, clovers, radish, cowpea and vetch. Information regarding effects or corn and soybean herbicides on these species is somewhat lacking. Herbicide label rotation restrictions often require substantial waiting periods before these species can be planted. These waiting periods are to assure that residual effects from the herbicide do not impact the following crop, the buyer (finished product) or livestock negatively. In some cases plants used as cover crops fall under the ‘other’ or ‘not listed’ category requiring the maximum duration before planting.
However, in recent conversations with the Office of the Indiana State Chemist we have learned the following. If the cover crop is not harvested, used as feed for livestock or sold in anyway and that the cover crop is terminated in the appropriate manner or left in the field, that the rotation restriction does not apply [personal communication Office of the Indiana State Chemist]. It comes down to the definition of a ‘crop’ and that a ‘cover crop’ is not really used as a ‘crop.’ Label rotation restrictions are in place for crops that are going to be harvested, cover crops are to be destroyed in the spring, left in the field or winter killed. The purpose is in having it there, but there is no finished product at the end of the season. However, because the company selling the herbicide does not recommend or approve a rotation other than the ones listed on the label, the company selling the herbicide is not liable for any injury or germination problems seen in the cover crop.