Great Bend Tribune
Part I
Published November 26, 2017
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, nonresidual 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 twenty 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.
Part II
Published December 3, 2017
Last week’s column discussed what happened with Roundup Ready® technology and the resistance problems that arose. Remember Roundup Ready® technology was developed to combat weeds that were becoming resistant to herbicide modes of action in current use. And with overuse across multiple crops, severe weed resistance issues developed with Roundup. Finally, since this problem was most severe and had the fewest options in soybeans, companies focused on genetically engineering soybeans. We are not discussing corn, wheat, or grain sorghum here. Wheat and grain sorghum weed control are being addressed in a manner not causing the problems that arose in soybeans. Corn also has other options and again these are not causing damage as with soybeans. This week we will focus on the solution developed and next week what very significant problems have arisen in a very short period of time.
There were/are herbicide chemistries very effective in controlling weeds that became resistant to Roundup (glyphosate). Weeds such as the pigweed species are very susceptible to chemistries like 2,4-D and dicamba (common name Banvel). These active ingredients are extremely effective in the control of many broadleaf weed species creating issues in soybeans. Unfortunately, broadleaf crops such as soybean, cotton, sunflower, and canola are very sensitive to these chemistries and not only couldn’t be used in the fields growing these crops but even in nearby fields as even a little drift can severely damage these crops. There is an old cotton joke that you could damage cotton simply by say 2,4-D in a cotton field. Both were/are being worked on but we will focus on the problem child this year – dicamba. These chemistries were chosen as they not only controlled the problem weeds but have been used for decades with little evidence of resistance issues.
The pesticide industry worked overtime developing a GMO soybean plant that would tolerate dicamba. GMO technology allows this but it isn’t as easy as it sounds. When Roundup Ready® technology first entered the market, there were very detailed protocols as to when it could be applied and when it couldn’t. As an example, for cotton Roundup couldn’t be applied after the first square, bud, appeared or the plant would lose those flowers, potential cotton bolls. Over time the genetics improved markedly allowing for broader application times. So over a period of years, soybeans were genetically engineered that were tolerant to dicamba. Please keep in mind that there is work on other broadleaf crops with both dicamba and 2,4-D tolerance. However, that was only one part of the equation.
Non-modified soybeans are extremely sensitive to this chemistry and while often not outright killing the plant can cause significant loss. Dicamba, unlike Roundup, is subject to what is termed vapor drift. This occurs when dicamba is applied where it is wanted but due to its chemistry can become a vapor when environmental conditions are right, reenter the atmosphere and drift from the field and damage off-site plants. 2,4-D can do this also. The second piece of the puzzle was to develop a dicamba chemistry more stable and likely to stay where you want it. After much work and EPA approval, the product was widely introduced this past growing season. As you might guess, things didn’t quite go as planned.
Next week – what happened, why, and what can be done.
Part III
Published December 17, 2017
This week will finish our discussion of the effects of weather on pest, specifically weed, control with herbicides. Remember that to combat the Roundup® weed resistance issues that were developing with Roundup Ready® crops new technologies were/are being developed to allow for the use of dicamba and 2,4-D herbicides on soybeans, herbicides that under normal conditions which would severely harm of kill soybean plants. The trouble with this technology, even with new and improved herbicide formulations, is that once applied they can become a vapor under certain environmental conditions and move off target. Sounds simple enough to avoid but it isn’t for the following reasons.
Since producers want to keep these herbicides on the fields they are spraying as they are applied, calm conditions are best. You can spray with “wind” and there are nozzles, sprayer adjustments, and products that can be added to the tank to allow spraying with a decent breeze. However, with these products applicators are particularly sensitive to doing their best to prevent physical drift. When are good wind conditions most likely, night and early morning, normally through about mid-morning. However, these favorable wind conditions lead to a problem.
Under normal conditions, air temperatures decrease with height. As you move from the soil surface and go up, on average, air temperature decreases by approximately 3o F for every 1,000 feet. As air from the surface rises, it is typically moister than the air above it and it cools more slowly so its temperature is higher than the surrounding air so it stays slightly warmer. This makes it buoyant and it continues to rise. A good analogy is the rise of a hot air balloon. When temperature actually increases with height a temperature inversion occurs. When this happens surface air that tries to rise is cooler than the surrounding air. It isn’t buoyant so it can’t rise and stays at the surface. The air “hugs” the ground. Foggy weather is an example here. This condition often occurs during late night through mid-morning, when winds are light. The last two paragraphs are the setup for weather leading to the problem.
There is one more component to add – temperature. Banvel, dicamba, is more likely to volatilize into the atmosphere after application as temperature increases – seventy to eighty degrees is perfect. So applicators trying to minimize the physical drift of the herbicide apply during calm to light wind conditions – early morning. Many late spring/summer mornings this corresponds with a temperature inversion in the atmosphere so surface air isn’t rising. And as the sun rises, heat is provided to the surfaces where Banvel was applied to. The chemical volatilizes from the surfaces it was applied to. If there are decent winds and no temperature inversion, the herbicide is dispersed and no or little damage occurs. If, however, winds are light and there is a temperature inversion, the volatilized Banvel will hug the ground and slowly drift to later be deposited up to several miles from where it was applied. If it lands on soybeans that aren’t dicamba resistant or other broadleaf species, severe plant damage occurs. This is exactly what happened to significant acreage this last growing season.
The public and private sectors of the weed control industry released extensive guidelines regarding ways to minimize this potential problem. Unfortunately millions of acres of soybeans were affected this last growing season, especially in Arkansas and Missouri but in all soybean growing areas. This led to regulatory agencies formulating new guidelines in addition to a significant amount of money paid out in clams.