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Tuesday, Jan. 24, 2017

Some old solutions to new weed-control problems

Posted Monday, October 24, 2011, at 4:00 PM

Weed resistance to herbicides has become a big problem. Weeds are the single most economically important pest producers have to manage according to Michel Owen, extension specialist at Iowa State University. And weed management is not what it used to be.

In 1997, researchers predicted that glyphosate resistance would not be a big issue in Round-Up Ready crops, but they underestimated a few weed species and resistance mechanisms.

The list of herbicide-resistant weeds continues to grow. Weed scientists are focused on the "driver weeds" that can potentially cause the more economic damage- Palmer amaranth, waterhemp and marestail (also known as horseweed). These three weeds are the weeds of major concern moving forward over the next five years as the infestation levels intensify and expand according to Bryan Young, weed scientist at Southern Illinois University.

Now weed scientists are discussing the possibility of using "dinosaur herbicides" as a solution for growers fighting weed resistance issues.

What they are discussing using are auxinic herbicides, such as 2,4-D with glyphosate as a short-term option to use in broad-spectrum, postemergence weed control. Since the 1950s, 29 auxin-resistant weed species have been discovered worldwide. In comparison, 21 glyphosate-resistant weed species have been discovered since 1996 when Round-Up Ready soybeans were introduced. What interests weed specialists is that two of the most problematic weeds in Round-Up Ready soybeans -- common waterhemp and Palmer amaranth - are not on the list of auxin-resistant weeds. There are three reasons that help explain why resistance to auxin herbicides has not become a big problem yet:

1. The auxin family of herbicides has a very complicated mode of action.

2. Resistance to these compounds is rare because a plant that evolves resistance may have a fitness cost or penalty to have resistance.

3. Auxin herbicides have rarely been relied on by themselves and are normally mixed with other herbicides.

There are concerns about going back to 2,4-D and other auxin herbicides because they are considered old compounds that tend to drift and move off-target to sensitive plants. Monsanto and Dow AgroSciences are working on new formulations to reduce drift and agricultural engineers are exploring spray application technology to reduce the problems also. Also some companies are working on developing new products with resistance to 2,4-D.

If you have huge resistance problems in your fields and are concerned about losing yield, the auxin herbicides may be a solution for now.

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As our local University of Missouri Agronomy Extension Specialist, Crook has been writing a column for the print edition Agriculture page for the past three years and we will now be sharing it on our web version. Crook has a bachelor and masters degree in agronomy from University of Missouri and received his doctorate in Agronomy from Kansas State University. He was in soybean variety development research for 22 years for various seed companies and has been Saline County's agronomy specialist for 10 years.
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