Glyphosate-Spawned Superweeds and Dicamba: The Connection

The herbicide dicamba has been causing massive crop damage in recent months, affecting farms from Colorado to Pennsylvania, and from Minnesota to Georgia. According to an August report from the University of Missouri, dicamba has destroyed over 3 million acres of soybeans, costing farmers millions of dollars in revenue.

This has left some mystified, because dicamba has been around for at least seventy-five years, used by commercial farmers and home gardeners alike. It is contained in a number of common weed killers, including Ortho Weed B Gon, Ace Lawn Weed Killer and Roundup Max – yet this kind of plant damage has never been seen before. What has changed?

Part of the answer to that question lies in the growing use of another Monsanto product, glyphosate. The use of glyphosate has skyrocketed in recent decades, creating serious problems, not the least of which is the development of herbicide-resistant “superweeds.

According to figures from the Department of Agriculture, between 89 and 94 percent of soy, cotton and maize (corn) crops grown in the U.S. today have been genetically modified to be “herbicide tolerant” (HT). Of the two herbicides commonly used, glyphosate became the most popular among farmers.

Unfortunately, noxious weeds such as pigweed (amaranthus retroflexus, or palmer amaranth) started becoming resistant to glyphosate. This led to a spiral in which farmers applied increasing amounts of glyphosate, which in turn caused weeds to become even more resistant, to the point that glyphosate was no longer effective.

In order to address this problem, Monsanto began engineering soy crops that were resistant to dicamba, an old standby. At the same time, the company developed a new formulation of dicamba. However, Monsanto began selling the new seeds before the new dicamba formulation was ready. Meanwhile, farmers started using the old formulations of dicamba on their fields, which chemical is more prone to “drift.” According to U.M. professor and weed specialist Kevin Bradley, farmers have also been using larger amounts of dicamba – and he doesn’t expect them to back off. 

That is part of the equation. The other part is that farmers today are spraying dicamba later in the season than they used to. Originally, the application of dicamba took place in April and May; however, these days, the herbicide is being used as late as July – when crops are more mature and thus more susceptible to dicamba damage.

Of course, Monsanto is charging more for its new dicamba-resistant seeds – another factor in farmers’ decision to stick with the old formulas. Now that the damage from those older forms of dicamba has become apparent, it remains to be seen if commercial farmers will be willing to pay more for dicamba-tolerant seeds.

In the meantime, dicamba manufacturers such as Monsanto and state governments are squaring off for upcoming legal battles over proposed dicamba bans and restrictions.


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