There are many reasons why cover crops had a so-so year in Indiana this past season. But if you tried them and blame fair to poor success on the cold snap in November or other cold snaps without snow, or on planting too late, you may be overlooking another possible cause that could be contributing to cover crop issues. And it is an issue which will have to be dealt with by those who are so serious about cover crops that they plan to continue using them even in tight economic times.
That group seems to be farmers who have grown cover crops for three or four years and seen the benefits already. The same group is also beginning to notice that herbicide carryover may be partly responsible for slow growth in the fall and some stand problems.
Barry Fisher, an agronomist and precision farming specialist with the Natural Resources Conservation Service, says that he believes there are real concerns with herbicide carryover affecting cover crops. The real concern is when residual herbicides are applied late. That is likely happening now as delayed applications of herbicides over soybean, and in some cases corn, may include residual herbicides.
Weed control experts are recommending residuals in many cases to help get the tough to control weeds. What you need to do, Fisher says, is make sure you read the chemical label, either before you use a residual, or if you have used it, before you buy cover crop seed this summer.
Some cover crops are more sensitive to herbicides than others. It depends on the cover crop and the herbicide. "We're finding that products that we used before and are using again as residuals have plant-back restrictions in many cases," Fisher says. "They've always been there- you just need to read the label."
In some cases those restrictions for coming back with a cover crop, even cereal rye, may be 10 months, more or less. Of all the cover crops, cereal rye seems to withstand chemical carryover the best. That's partly because it can be planted later, after more time has elapsed, although it's still nowhere near 10 months after herbicide application.