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Serving: Central

Palmer pigweed ‘driver weed’ in soybean, cotton fields

A farmer sent me an e-mail regarding the pigweed situation, writing jokingly, “The only positive thing about the pigweeds overgrowing my soybean fields, is they eliminated my marestail problem.” That is an excellent definition of a driver weed. Palmer pigweed is definitely our driver weed in soybeans and cotton.

That is what is wrong with the argument, “I cannot leave glyphosate out of my herbicide mix because it controls 200 weed species or whatever the number is.” So does Palmer pigweed. If you do not control it, it does not matter what other weeds glyphosate kills. That is why it is so important to save the Roundup Ready technology and to do so requires diversity.

The farmer also wrote that in fields that were too grown up to harvest he could cut shooting lanes and lease the field for deer hunting because the pigweeds make excellent cover for deer. His third suggestion was to selectively breed for the 6- to 8-foot pigweeds that make the nice uniform branches and market them as Christmas trees. Farmers have to have a good sense of humor.

About deep tillage and tillage in general for pigweed control, I think there is a lot to be learned and a lot of it will be learned by farmers. I hear some blame no-till for our pigweed woes. Perhaps it has contributed; perhaps it has not. Back before Roundup Ready when we were fighting Palmer pigweed the first time (although in a much smaller geographic area), we were pretty much in a conventional tillage system. Most of our residual herbicides then were incorporated — which required preplant tillage — and most were in wide rows and cultivated. It was Roundup Ready that allowed the successful shift to no-till and other forms of conservation tillage as well as the successful shift to narrow rows.

The pigweeds came in and were doing fine in the conventional tillage program and in my opinion just getting ready to rapidly spread across the state when Roundup Ready came along. Some of my counterparts to the north have suggested we just need to go back to cultivation and our problem will be solved. I do not believe that for the reasons cited above. However, some diversity in our tillage programs could help.

When it comes to deep tillage, there are some things to learn. Pigweed seeds germinate from very shallow depths. If you bury the seed deeper than they will germinate, they obviously will not come up — at least that year. The scientists are also saying that they do not appear to remain viable in the soil as some other weed species. If you bury them deep and do not disturb them for several years, perhaps they will lose viability. If that is the case, moldboard plowing would seem to be a better option than deep tillage using chisel plows or similar tools.

It would also seem that if you bury the seeds you do not want to stir them back up. Therefore it might not work where you are bedding. If you bury them this year, how long should you wait before you deep-till again? There would seem to be an excellent research project there for academic weed scientists and also some options for innovative farmers to play around with.

Moldboard plowing was the first thing that came to mind when the farmer called and told me he had rented a farm that did not have a combine put in it last year due to pigweeds. Perhaps that would give him the fresh start needed to turn things around. I completely agree with the University of Arkansas weed scientists’ program of zero tolerance or soil seedbank management. You have to get the seedbank numbers down, or keep them low if you are not grown up yet, in order to win the fight. As long as the seedbank numbers are such that 95 percent control still means a crop failure, you are in trouble.

I do not believe all of the answers will come in the next new jug or the next new trait. We can not keep up with the pigweeds in that paradigm. Farmers will ultimately win, but I predict that five years from now we will be using several weed control methods in addition to herbicides and traits to accomplish this.

TAGS: Cotton
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