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Mississippi: Glyphosate Resistant Weeds Are Bad, But Soil Loss Worse

Debra Ferguson
By Ernie Flint, Area Agronomist, Mississippi State University Extension Service April 21, 2012 11:14

Herbicide resistance in some of our most competitive weeds has proven to be one of the greatest challenges to agriculture. Every year we learn of new weed species. We have come to believe that certain products are necessary for growing crops, at least on the large scale we have come to accept as the norm. However, we are being forced to modify the crop production systems that have evolved over the past two decades or more.

The “keystone” of this dilemma is that more and more weeds are becoming resistant to the herbicide glyphosate. When we began hearing stories about glyphosate resistant horseweed, most people chose to ignore it since this was not a weed we normally considered as competitive in our crops. A trip across Missouri about 7 years ago convinced me that our perception of this weed was incorrect, and now we have it in abundance in most of our crop production areas.

Since that time, other weeds have entered the ranks of glyphosate resistance, with some having resistance to multiple classes of herbicides. I will leave the technical aspects of this subject to the weed scientists, but I do see the issue from the farmers’ viewpoint. The reality of herbicide resistance has in their view become an extremely difficult problem that threatens profitability, farm sustainability, and ultimately the ability to continue farming.

Herbicide resistance in weeds like horseweed, pigweed(s), Johnsongrass, ryegrass, and others is threatening to change our production systems in very dramatic ways. Some growers have returned to conventional tillage after years of reduced tillage and no-tillage farming. Herbicides that have not been used on a large scale in decades, such as trifluralin, are being returned to service as a way of preventing the emergence of these “monster” weeds.


A “background” issue in this discussion is that of compromised soil conservation practices. The great achievements we have seen in the reduction of soil and nutrient loss are being challenged by the perceived necessity for a return to tillage as means of dealing with weed resistance. This issue is in fact as big a “deal” as the more apparent problem of weed resistance since it impacts long term sustainability. Simply said, “if we lose our soil, we’re finished anyway.”

A current discussion among some of the producers I work with is how to deal with resistant Italian ryegrass on sloping fields that are very susceptible to soil erosion. The need to avoid tillage on these fields is very evident, but planting through ryegrass is not a viable option. One suggestion has been to apply strong pre-emergence herbicides in the fall as a means of keeping fields “clean” through the winter months. While this may be preferable to tillage, this method will lead to increased soil loss. We need to find an alternative that will solve this question.

One method may be to plant a cover crop such as wheat, then apply broad spectrum herbicides commonly used in that crop. There are a choice of materials, which would need to be evaluated for effectiveness and tolerance of summer crops planted after the wheat stand is destroyed. This system would likely have multiple benefits of the desired suppression of weeds, soil stabilization, conservation of nutrients, and increased soil organic matter.  In some years, the grower might also choose to harvest the wheat for grain if prices supported that decision.

Others may find holes in this idea large enough to drive a bus through, however we have to begin work toward not only growing crops profitably but also protecting the land for the future. This method, or some other idea, may already be in use somewhere, if so, I hope to talk with those who have made it work. Either way, we have to try other methods before we return to the destructive farming methods of the past.

Thanks for your time.

Debra Ferguson
By Ernie Flint, Area Agronomist, Mississippi State University Extension Service April 21, 2012 11:14