There’s no doubt that much of the rapid increase in no-tilled acres over the past 20 years is due to the extensive use of glyphosate-resistant corn and soybeans. Yet, extensive reliance on this single herbicide mode of action may be holding back the future growth of no-till. Even more worrisome is the impact it could have on simply maintaining the no-till acres we already have.
A report from the Council for Agricultural Science and Technology argues that glyphosate-resistant weeds pose one of the most significant threats to the future growth of notill. The scientists who authored this report say these concerns are already forcing some farmers to modify their conservation-tillage practices and even rely on more tillage to overcome these serious resistant weed worries.
Future No-Till Concerns
The report’s authors even go so far as to point out the herbicide-resistant weed situation could undo much of the good no-till has brought to North American agriculture and the environment over the past 5 decades.
While scientists and growers have long recognized both the beneficial and detrimental aspects of tillage, glyphosate sharply reduced the role of tillage in controlling weeds under no-till conditions. This has taken place on a huge scale, despite the first instance of glyphosate resistance that showed up in several no-tilled soybean fields in Delaware back in 2000.
But even before then, we knew here were weed-resistance problems with glyphosate based on the earlier experiences of Australian growers.
Over the past few decades, extensive glyphosate usage has led to the abandonment of numerous tankmixes, reliance on fewer herbicide modes of action and the reduced use of preemergence- applied residual herbicides.
Yet glyphosate certainly doesn’t stand alone when it comes to issues with herbicide resistance. In fact, resistance to a number of herbicides has been confirmed in nearly 200 weed species around the world. One-third of these weeds are found in the U.S.
Unfortunately, today’s options with no-till seem to be limited. They include doing more tillage, making more effective use of alternative or new herbicides and looking at making changes in our overall cropping programs. But using any of these options will likely lead to higher costs, require more field labor, increase fuel needs, have environmental implications and reduce the possibility for no-tillers to expand their acreage.
Is Plowing Inevitable?
One of today’s biggest glyphosateresistant worries among no-tillers in Ohio, Illinois and other areas of the Corn Belt is the rapid spread of Palmer amaranth. Already a concern in the Southeast, it has led to conventional tillage regaining its rank as the dominant tillage practice with glyphosateresistant cotton.
Glyphosate-resistant Palmer amaranth was discovered in Georgia in 2004 and has even led a number of the state’s growers to abandon cotton production due to their inability to manage these resistance weeds. In some instances, herbicide alternatives to deal with these resistant weeds have cost $60 per acre.
Yet by moldboard plowing, these cotton growers have reduced Palmer amaranth emergence by up to 60%.
Time For Action
More research, development of new herbicides and better weed-resistance management practices are needed if we are to continue to expand our notill acres. In the past, no-tillers have found the almost universal use of glyphosate represented an effective, efficient and consistent way to control weeds with less tillage. But our thinking and overall reliance on a single herbicide mode of action has to change. Crop rotations also need to be expanded and utilized more effectively.
Maybe we’ll find a more effective weed-control solution with the expanded use of cover crops. While some purists don’t feel vertical tillage has any place in a no-till system, could this limited-tillage tool have some benefits in dealing with resistant weeds?
In the past, we’ve always found the answers to make no-till more effective, and I’m sure we’ll continue to do so. But we’ve got to find new solutions to deal with growing herbicide resistance that threatens our ability to make further advances with no-till.