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Baldwin: Weed shifts fueled herbicide boom years

When I began my masters degree program in 1969, there were already a lot of herbicides on the market. The transition from hand weeding to the herbicide era had been made. I honestly cannot remember if the introduction of a single herbicide like Treflan ended hand weeding in cotton or if it transitioned out — but it ended. Treflan introduced the dinitroaniline or DNA mode of action and other herbicides in this family such as Planavin quickly followed.

Diuron or Karmex had introduced the photosynthetic inhibitors in cotton and others such as Cotoran soon followed. These could be used pre-emergence and also as post-directed sprays. MSMA and DSMA had also come along to help with postemergence grass control.

Another very important herbicide mode of action had been introduced with Lasso for use in corn and soybeans. It provided weed control similar to Treflan but could be applied to the soil surface at planting.

I mentioned in a previous article that atrazine had been introduced in corn. It is another of Ford’s Hall of Fame herbicides. Atrazine for broadleaf weed control combined with Lasso for grass control was one fine weed control program. Following Lasso were other herbicides in that family such as Dual, which is still widely used today.

In rice the herbicide selection was limited to the phenoxies, propanil and molinate or Ordram. However, an effective program could be built around these in the day.

In soybeans we had Treflan and then Lasso, which both were excellent herbicides for grass and pigweed control. Also because of the large market potential in the United State, the emphasis on herbicide development in soybeans was huge.

The herbicide boom had begun. We were bumping along in the late 1960s and early 1970s controlling our major weeds — annual grass and pigweed — nicely with herbicides supplemented with cultivation. All of the soybeans were still grown in wide rows for cultivation.

We learned very quickly that weeds adapt. When Treflan, Lasso and other early herbicides effectively controlled the grass and pigweed problem, we started seeing new weeds. That is a different principle than resistance, but the end result is often the same — you wind up with weeds you cannot control. That principle is called species shifting.

I was actually taught by well-meaning professors in the day that we would never have herbicide resistance because weeds did not make new generations quickly enough to adapt like insects had to insecticides. That was the best information we had at the time, but it turned out to be wrong.

Species shifts began to occur and we saw new problem weeds such as prickly sida (teaweed), cocklebur and morningglory in soybeans and cotton and sprangletop in rice. I vividly remember a slide photo Dr. George Mullendore, the famed cotton agronomist from Mississippi, used to show in some of his presentations. It showed a farmer pouring Treflan into his spray tank through a cloth strainer in an attempt to “strain the teaweed seed out of it.” He was obviously convinced his new weed was coming in the Treflan and did not understand the principle of species shifting. By the way, Mullendore’s weekly Delta Farm Press column “Report from the Field” was a tremendous influence in my formative years and is one of the main reasons I have written this one for nearly 40 years now.)

So the herbicide boom was really on. Everyone wanted a piece of the action and we began a cycle of getting an effective herbicide or group of herbicides, over-using them, getting a new weed, finding a new herbicide that would control it, getting another new weed, etc. The thing we had going for us was the herbicide pipelines were full. There were a large number of companies screening new herbicides.

We had an early herbicide screening program at the University of Arkansas that was essentially one professor’s research program. We could not manage enough graduate students to properly evaluate all of the new herbicide candidates to write recommendations for them. Life was good for both farmers and weed guys.

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