First a very Happy Thanksgiving weekend to all and safe travels to those on the road. With a holiday weekend, instead of a deep or heavy topic, let’s discuss the weather. Specifically weather effects on pest control. This is a very broad topic so for today, what role do weather conditions play in the use of pesticides? This has become an area of greater interest with the continued development of genetically engineered crops for more effective weed control. This week sets up what has happened and why.
Herbicides come in various modes of action, how they kill weeds, and various types of formulations. When the same mode of action is used repeatedly on a given field, the weed or weeds often develop resistance to the given chemistry.
We effectively change the genetic makeup of the species by eliminating plants susceptible to the herbicide and favor those few that are resistant. In essence we change the genetic makeup of the plant to render the herbicide ineffective.
Starting in the mid-1990s through today, the industry developed crops resistant to glyphosate, the chemical in Roundup. Today we have Roundup tolerance in a variety of common crops: soybeans, corn, canola, cotton, and alfalfa. The advantages to glyphosate are many. Many common broadleaf and grass weeds had developed resistance to herbicides in use for decades.
It was becoming very difficult to control grass weeds in grass crops (corn, sorghum, etc.) and broadleaf weeds in broadleaf crops. Grasses such as crabgrass species and shattercane were becoming more problematic in corn. Pigweed species and many other problem broadleaf weeds were becoming increasingly difficult to control in crops such as soybeans, cotton, and alfalfa and control was expensive.
Roundup is a nonselective, non-residual herbicide that kills most grass and broadleaf weeds. And as will become apparent later, it doesn’t volatilize so once applied it stays where it is applied. Unfortunately, it was also effective in killing crops so it couldn’t be used once the crop had emerged except with special shielded sprayers. The advent of genetic engineering allowed the promise of making crops resistant to herbicides that would normally kill or severely injure them.
So over 20 years ago, Roundup Ready crops were introduced and quickly grew in popularity with their effectiveness, no need for other more expensive herbicides, relatively low cost, and low environmental risk. For corn, soybeans, and cotton the market was rapidly dominated by these crops. This technology was one of the reasons that no-till acreage was able to increase so rapidly during this period. What could go wrong?
We failed to observe the lessons learned previously and over time scattered areas showed a few weeds no longer controlled by Roundup. Scattered areas grew into larger and larger areas and a weed species or two that developed became dozens and then hundreds across the globe.
There were answers. Producers could resume tillage for weed control which wasn’t very attractive for several reasons but started to happen. They could use other, relatively expensive chemistries for control but these were often not as effective and had problems associated with them. And while these problems existed for both grass and broadleaf crops, the lack of options was most acute for soybeans and broadleaf crops.
Or the herbicide industry could genetically engineer crops to allow the use of herbicides normally damaging or killing the crop. This was the option that was deemed preferable and most profitable for all concerned. Notice there is no discussion of wheat or grain sorghum as GMO Roundup Ready versions of the crops were never released.
Next week: What happened and why.

Dr. Victor L. Martin is the agriculture instructor/coordinator for Barton Community College. He can be reached at 620-792-9207, ext. 207.