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.

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