Palmer amaranth pigweed

What it takes to defeat herbicide-resistant weeds

Winning the fight against herbicide-resistant weeds is going to require much more respect for the adversary at all levels — from researchers to agribusinesses to farmers. The age thing gives me a different perspective because this is Round 2 for me in the Palmer amaranth fight.

In my very early career I was totally focused on cocklebur and morningglory control. Pigweeds as we had known them had disappeared with the use of superb new herbicides like Treflan and Lasso. Sometime in the early 1980s, farmers in northeast Arkansas began complaining they were not controlling pigweeds with Treflan anymore.

I initially blew it off to improper rate or poor incorporation. As the complaints continued, I decided to set up a demonstration up there to “show them how to do it.” When I went to evaluate my treatments for the first time I quickly removed my University of Arkansas signs, told them to disk it up before anyone else saw it, and got out of there before anyone else saw me! I never forgot that day.

We realized at that point we had a new pigweed, Palmer amaranth, and it was a much different cat than the pigweeds we had dealt with before. We also realized we had Treflan (DNA)-resistant Palmer amaranth. I am a poor plant taxonomist, but that weed got my immediate attention.

Within a two- to three-year period it was rendering fields in the area where it occurred non-productive. It simply overpowered all herbicide treatments and all other weeds in the field.

In spite of my embarrassment in the story described above, I established a research location in a grower field that had essentially become impossible for them to farm. The ALS-inhibiting herbicides came out and Scepter proved to be a very effective Palmer amaranth herbicide — for two years. It blew up before we ever knew what hit us. In hindsight that should have taught us far more than it did.

At that time we were actually being forced outside the box and beginning to look at cover crops and other integrated approaches. Then Roundup Ready came along and the problem was solved, or at least we thought it was. The most fun field day I ever conducted was the first year we had Roundup Ready soybeans at that Palmer location. We could kill them from 3 inches tall up to any height we could get the boom over!

Palmer amaranth and water hemp have all the attributes to be nightmares. The genetic diversity is off the scale. I have never seen a drought-stressed Palmer. Seed production is off the scale. It germinates all season and the list goes on.

After we first started seeing a few escapes in Roundup Ready fields around 2005, many folks said, “I can’t believed it happened so fast!” How many weed scientists, industry reps and farmers are now saying about the PPO inhibitors, “I can’t believe it happened this quickly?”

Is there a pattern here? Will it be any different with the next herbicide we over-rely on or the next? The complacency and denial continues to baffle me. Roundup Ready changed the face of agriculture in our country. Palmer amaranth, water hemp and other weeds have the capability to change the face again — in the wrong direction.

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