This week I am pleased to have as my guest writer, Dr. Gordon Vail with Syngenta. Dr. Vail and I have had a long history of working together, dating back to our early days when we worked with Dr. Vail on herbicide efficacy. Recently I talked to Dr. Vail about herbicide resistance and I found his comments unsettling, especially for the future of weed control as it relates to no-till.
Good to the Last Drop?
Will Herbicide Resistance Cripple No-till?
No-till is considered a key practice for controlling soil erosion, but it is hard to imagine an effective no-till system without post-emerge herbicides. Herbicide resistance could herald dire consequences for no-till, one of the primary practices in combating soil erosion.
Have you ever stopped for a minute to think what corn and soybean weed control would look like on your farm without the use of post-emergence herbicides? I challenge you to think about it for a minute because it is a sobering thought. It has been more than 16 years since we saw the last new herbicide mode of action registered. That mode of action first discovered in the late 1970s was the HPPD inhibitors (e.g., Callisto® herbicide). There have been a multitude of new inventions since then that have revolutionized our lives, yet a new herbicide mode of action hasn’t been one of them.
Imagine trying to control waterhemp, giant ragweed, Palmer amaranth or marestail in crops without a post-emergence herbicide. This is certainly something that I don’t want to see, but we are headed toward this reality at an alarming rate in corn and soybean production. We continue to see repeated reliance on post-emergence herbicides, a practice that advances the evolution of herbicide resistance in these very difficult-to-control weeds. In addition, we are seeing abuse of these herbicides, including less-than-labeled rates being applied to larger–than-labeled weeds. As a result of this repeated use, waterhemp is now resistant to six of the seven post-emergence herbicide modes of action we rely on for weed control in corn and soybeans. Even more concerning is that some waterhemp populations are resistant to multiple modes of action, which make them even more difficult to control.
My intention is not to alarm but to make you think differently about your approach to weed control. While industry is actively searching for new herbicide modes of action, none are on the horizon, which means you have to manage your crops with the herbicides you have for the foreseeable future. If your weed control strategy relies exclusively on herbicides, you are at significant risk for losing the ability to use post-emergence herbicides.
While this may sound dire, there are things that can be done to ensure the long-term viability of post-emergence herbicides. The first step is to include some non-herbicide strategies (e.g. crop rotation, cover crops) into your weed control program to reduce the pressure on the development of herbicide resistance. The second step is the use of pre-emergence herbicides at full rates. Pre-emergence herbicides are important because weed resistance to these herbicides is not common, so they are still quite effective. The last step is to use herbicides with multiple, overlapping modes of action and apply them timely and according to the product label.
While herbicide resistance is changing how many growers are farming these days, it can be managed with a few critical steps. Don’t let herbicide-resistant weeds control how you farm. Instead, make how you farm control the resistant weeds.
Gordon D. Vail, Ph. D.
Technical Product Lead