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Glyphosate-resistant Palmer need not be crisis

Back in early June, I was walking in a number of cotton fields observing the glyphosate-resistant Palmer amaranth control with a crop consultant.

He went through the laundry list of herbicides used on the over 1,000 acres we had observed. The list included Reflex, Gramoxone Inteon, Caparol, Ignite and Dual Magnum. The cotton was about to put on the fifth true leaf at the time, and it dawned on me that glyphosate was not mentioned.

I am a history buff, and landmark change like this is striking to me. Just six years ago that consultant would have been talking about applying the third glyphosate application on that cotton before the fifth true leaf was the size of a quarter.

Just three years ago he would have been talking about at least two glyphosate applications on the Flex cotton.

Now that we are in the era of glyphosate-resistant weeds, glyphosate, even though it is at a historic low price, was not even on his radar screen.

I really feel that all the Tennessee agricultural Extension agents, crop consultants and retailers fully realize we are going through a landmark weed control change and are doing the best job possible trying to manage glyphosate-resistant weeds. I feel only about 40 percent or so of Tennessee growers fully realize that we are in the process of a historic change, and that they will have to manage multiple glyphosate-resistant weeds now or in the near future.

I talked to a farmer from Haywood County, Tenn., last week, and he told me that despite listening to me at meetings and reading all the press, he was skeptical that there was Palmer amaranth that glyphosate could not control.

He told me as of this week he is a true believer. What caused the change was that several of his neighbors have cotton fields covered in 1-foot to 2-foot tall Palmer amaranth despite multiple glyphosate applications. Some of these neighbors had tried to rescue these fields with an application of Ignite because they had WideStrike cotton.

They burned the Palmer, but all of it was re-growing. He realizes he will be fighting it all year and will likely spend a lot of money on herbicide and still lose significant yield to competition. Though he was skeptical, he did heed our advice and use pre-emergence herbicides on his cotton. The result is his cotton is clean of Palmer and his neighbors’ fields are not.

I really do not blame folks for being skeptical of the latest crisis. My favorite is all the fuss over global warming. Despite all the experts using complex computer models about how the planet is warming, we just went through one of the coldest, snowiest winters in 40 years.

I have written and used computer models as well in graduate school. I have found them to be poor prognosticators. However, glyphosate-resistant Palmer amaranth is not a prediction of a computer model. It can easily be observed in many west Tennessee cotton and soybean fields.

Over the last week I have talked to a number of very frustrated retailers in areas where glyphosate-resistant Palmer amaranth was fairly widespread last year. The reason they are frustrated is that they continue to be asked by growers in that area to clean up 12-inch to 18-inch Palmer in their just-emerging Roundup Ready soybeans.

Only glyphosate will control Palmer that large. However, the Palmer must be susceptible to glyphosate to be controlled, and most of it is not.

Moreover, some growers were trying to lightly till large glyphosate-resistant Palmer amaranth. What ended up happening is they buried about 14 inches of an 18-inch tall Palmer amaranth. Again, nothing is going to control a large buried Palmer, including Gramoxone Inteon.

I do not believe that glyphosate-resistant Palmer amaranth has to be a crisis. I have seen it managed well in many cotton and soybean fields in west Tennessee. In these fields, a pre-applied residual herbicide was used to control it early, followed with a post application before the Palmer became 4 inches tall.

Obviously, applying that post application timely can be easier said than done. I do not believe we have the sprayer power in the state to make every post application as timely as needed. That is why the pre-emergence herbicides are so critical. However, glyphosate-resistant Palmer amaranth can become a bit of a crisis when growers are in denial that it will happen in their fields.


TAGS: Cotton
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