The Ever Growing Importance of Residual Herbicides

The Ever Growing Importance of Residual Herbicides
Dan Klavetter, Agronomy Sales, Stewartville
(507) 272-0157

$286 million. That is the price tag to bring a new herbicide to market. That cost is nearly double from the year 2000. With low commodity prices and high expenses in all aspects of the agriculture industry, it’s no surprise that research and development for new chemicals has slowed and the pipeline for new herbicide modes of action, or even sites of action, look bleak. The last site of action discovered was the HPPD Inhibitors (Laudis, Halex GT, Acuron), which was close to 30 years ago. Even if a new compound were discovered today that showed potential to be used as a herbicide, it would be subject to an average of 11 to 15 years of trials, testing, and regulatory hurdles. This has forced the industry to combine products with multiple sites of action in order to combat or slow down herbicide resistance.

It was recently discovered that palmer amaranth has made it to Minnesota. Yellow Medicine and Lyon Counties have inherited the weed by way of conservation seed mixes. The lack of regulation on this category of seeds and the increase of acres that went into CRP programs should have every farmer’s radar up. At palmer’s most rapid growth stage, it can grow up to 4 inches per day and reach a maximum height of over 6 feet. Most of our post herbicides work best when weeds are in the 4 to 6 inch height range. In palmer amaranth’s case, there would be one day to make a herbicide application an effective one.  The best way to control palmer is the equivalent to controlling waterhemp, which is layering out residual herbicides to affect germination. We can still do a decent job of cleaning up some emerged weeds and escapes with a post spray, but when there is a green carpet of weeds to battle in the field is where there is management trouble.

Weeds are also adapting to what is sprayed as well; most waterhemp is ALS (Pursuit), and glyphosate resistant, but now in this area, the University of Minnesota has also discovered some PPO (Flexstar) resistant waterhemp.  Waterhemp, pigweed, and palmer amaranth are all very closely related to one another and reproduce by cross-pollination with one another. This allows herbicide resistant traits to spread between the species faster than usual. Placing a strong emphasis on residual herbicides and layering them during the germination window is the best chance of success of weed management. The benefit to palmer, waterhemp, and pigweed being related is the residual chemistry chosen for one will be very effective on the others. Deciding to use residual herbicides on waterhemp now will allow for better management of palmer amaranth as it reaches new areas. Taking a proactive approach now, instead of reacting to a weed problem later, can save farmers headaches down the road as weed management becomes increasingly difficult in the future.

As we creep closer to spring, let’s be sure that we have an effective plan in place that includes residual herbicides. Contact your local Progressive Ag Center agronomist if you would like to discuss this further. Thank you for your business and please have a safe remainder to your winter season.  

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