Weed Science 101: Making new technologies work: Part I

What a difference a year makes. At last year’s Northeast Research Station Field Day, speakers couldn’t say much about the new dicamba- and 2,4-D cotton weed control systems that were being tested at the station near St. Joseph, La.

Since then, the Roundup Ready Xtend cotton and soybean traits and the Enlist Duo soybean traits have both been deregulated by USDA, and Donnie Miller, LSU AgCenter weed scientist and resident director at the Northeast Station, was free to talk about them at this year’s Crop Production and Pest Management Field Day on June 17.

Almost to a row, the plots sprayed with Roundup Ready Xtend or Enlist herbicides were mostly weed-free, but Dr. Miller, who has been working with both systems for several years under confidentiality agreements, says there’s a reason for that.

“These technologies, obviously, are new even though we’re talking about older chemistries that have been around for a long time,” he said. “Just because they are new technologies, and they’re exciting, does not mean they do not conform to the rules of weed science.

“It’s just like any other weed management program out there – if you use it the right way, you’re going to be very happy with it, and it’s going to be all smiles. If it’s used the wrong way, labels are not followed, there’s going to be some issues, and there’s going to be some hurt feelings and so forth.”

Each of the plots was sprayed with a pre-emergence herbicide at planting or if they didn’t have a pre-emergence application, they were sprayed early postemergence with dicamba or 2,4-D with another herbicide tank-mixed with it.

“As we walk through, you’re going to say ‘Donnie, you’re showing us plots that either look good and just need a little follow-up to clean up or look good right now and are going to need a little follow-up a little later. But for the most part they look good.’”

That’s by design, he said. “These technologies are not going to be any different from the others, and I don’t think any of the companies are going to just push them by themselves – just come out with Xtend, just come out with Engenia, just come out with Enlist. Don’t worry about anything else. I think we learned our lesson with another technology that that’s not the way to do it.”

Mother nature is always going to win with Palmer amaranth or pigweed providing an example. Glyphosate-resistant pigweed did not show up in Louisiana as early as it did in other southern states, but it’s been making up for lost time.

“The past few years it’s been catching up with us,” said Miller. “You go down the roads, the ditches and the fields, and you see a pigweed here and a pigweed there. We’ve talked about pigweed at length with the number of seed we have, and the issues it can produce.”

Most herbicide and technology companies and weed scientists will agree, he said, that the best way to mitigate resistance “is to never let these weeds get off the mat. In other words, you want to include residuals, you want to include every bullet in every arsenal you have so we can continue to use all the technologies we have.”

Producers should “layer” their weed control protection, he noted, by putting down a residual herbicide with their burndown application in the spring, a pre-emergence herbicide at planting, a postemergence application with a residual herbicide and come back with a layby herbicide.

“You always want to have something out there to where you can get the crop to be your natural defense and provide shading and a natural residual,” he said. “That’s our best defense against resistance issues – multiple modes of action, residual where you can use them and never let these things go to seed.”

For more on herbicide-resistant crops, visit http://agron-www.agron.iastate.edu/Courses/Agron317/2005/readings/HRCresistance.pdf

TAGS: Soybeans
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