The story of the development of weeds that are resistant to herbicides is one which deserves documentation since it is an almost direct reaction to the adoption of herbicide tolerant crops in American agriculture. One of the most interesting parts of this story has been the way this challenge has been dealt with by producers from its earliest onset until today.
The problem of herbicide resistant weeds might have been managed much better had we accepted that it was a real problem very early. Instead, many producers passed it off as if it were something that would not affect them, or that if it ever did they would be able to deal with it somehow. Nothing could have been farther from the fact since the arrival of resistant weeds in new areas each year did not seem to increase the level of awareness among producers even though weed scientists made great efforts to inform them.
Very few serious efforts were made to stem the flow of the seeds of these weeds. Even though growers were reminded to take precautions against the movement of equipment from infested areas this mistake was made over and over. Growers who actually found resistant weeds on their own farms seem to forget this when harvest operations got into motion, moving equipment from infested fields into clean fields almost oblivious of the issue.
The transfer of equipment from one grower to another across state and county lines has been a contributor to the movement of resistant weeds. We have become fully aware that a wash and wax job on a combine or other implement does not prevent the movement of the seeds of marestail (horseweed) or pigweed. The exchange of rental property has also been a source of contamination since the old renter may have known of the presence of resistant weeds but may not have taken the time to make sure the new renter was informed of this fact.
Natural movement of seeds is of course at issue as well. I think we all know that the problem of resistant weeds would have made its way across the country even without the farmer’s assistance since these seeds are carried by wind and wildlife, especially birds.
They are carried by water as streams overflow their banks into uninfested fields. In some cases only the pollen from a resistant plant need be moved in order to transfer the problem. The precautions we could have taken might have added years to the time required for these noxious plants to arrive in Central Mississippi, but they probably would have arrived anyway.
My first introduction to weed resistance was in 2002 as I moved a daughter to a school in Kansas City, MO. I actually stopped to walk in fields of marestail that had overcome soybeans in the western part of Missouri. My full awareness of resistant Palmer amaranth arrived later along Highway 1 in Coahoma County where I stopped to walk in a field where cotton could not be seen for the overgrowth of this resistant weed.
Currently, growers in the Hill country of Mississippi are dealing with resistant marestail and pigweed. Five years ago these growers did not really accept that these problems would ever reach them, but they are here today. Now we have to deal with them just like others have with crop rotation, residual herbicides, new herbicide technologies, cover crops, and something I had hoped would not be needed – tillage. We will learn to deal with these problems, but they have made farming a lot more complicated.