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Research field - controlling resistant weeds

A few weeks ago I attended a University of Arkansas field day at Widener, Ark., to hear about glyphosate-resistant Palmer pigweed and how to control them.

The research site is in a grower field where, like so many other examples, the resistant pigweed population had exploded to the point the farmer essentially lost the fields the previous year.

The grower is an excellent farmer I have known for over 30 years and he is also an excellent speaker. He opened the program talking about how he had gotten into the situation while thinking he was doing things right.

In 2009 he spent $50 to $60 on herbicides in his Roundup Ready program and harvested 20 bushels-per-acre soybeans, due to the solid infestation of pigweeds. Based upon yields and herbicide costs in nearby fields that did not have the problem, the pigweeds cost him $200 per acre.

At the field day were large field demonstrations and small plot research with both Roundup Ready and LibertyLink soybeans. The small plot studies had a resistance confirmation study and pigweeds growing healthy after a 176-ounce rate or Roundup WeatherMax.

There were also small plots where the pigweeds had been effectively controlled in Roundup Ready soybeans by integrating soil residual herbicides along with very timely applications of conventional postemergence herbicides, especially Flexstar.

In the LibertyLink studies were clean plots where they either made two applications of Ignite or they followed a residual herbicide with one application of Ignite. The interesting thing about the LibertyLink plots is it really did not make much difference which residual herbicide was used as long as they made the timely application of Ignite.

At the stop for the large plots, they had a split field where half was planted to LibertyLink soybeans and the other half to Roundup Ready soybeans and best management practices were used in each. Both sides of the field (that was overgrown last year) looked very good.

It makes a good point that pigweeds can be controlled in both systems. We are going to have to do that on a lot of acres that for the next several years. However, the speaker made the point that the LibertyLink program can be more forgiving because there is a little more flexibility in the application timing compared to the herbicides like Flexstar. Also you can make two applications of Ignite in the LibertyLink soybeans whereas you can only make one Flexstar application and be within the label.

With the conventional herbicides in the Roundup Ready program, if you make a bobble the program will fail. The LibertyLink program can fail, too, but it takes a bigger bobble.

I am all for diversity and making effective use of all of our technologies. However, we must find a way to reverse the current trend we are in. I believe the LibertyLink acreage in the Mid-South will increase as fast as seed production will allow. However, in the name of cheap glyphosate, we are abusing the Roundup Ready program until it doesn’t work and then switching to LibertyLink.

Trying to get another year or two out of a Roundup Ready program by using conventional herbicides, when you know you are in trouble, is like trying to cure cancer with a Band Aid. You use up the Roundup Ready technology and then are forced to start abusing the LibertyLink technology.

We have to find a way to get a much larger acreage of LibertyLink soybeans planted in fields where the problem has not yet occurred. Then you keep both technologies viable in that field. We need every farmer to have the philosophy that some are adopting and that is treat every field like it has a resistance problem. That means diversity in crops, diversity in herbicides and diversity in herbicide tolerant traits so you can rotate non-selective herbicides like glyphosate and Ignite in a truly effective manner instead of a fire fight.


TAGS: Soybean
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