There is a growing resistance movement happening all across America. Except this one is taking place in the fields, not in the streets, in the form of herbicide resistant weeds and it has been quietly, but aggressively, growing for years. This movement has been expanding despite diligent efforts of spraying more of the same herbicides and more toxic herbicides.
The movement’s latest location has been Nebraska where scores of 2,4-D herbicide resistant waterhemp have been occupying the State’s fields.
The University Nebraska-Lincoln reported in October that:
Waterhemp plants treated with up to 64 times the recommended rate of 2,4-D were stunted, but recovered to produce seed.
Already notoriously hard weed to control, this resistant waterhemp, a pigweed (Amaranthus) species that is capable of producing more than 1 million seeds per plant, has evolved resistance to other herbicides. The University noted that:
Since 1993 waterhemp populations have been reported to have evolved resistance to atrazine (Photosystem II inhibitors), imazethapyr and chlorimuron (ALS-inhibitors), fomesafen and lactofen (PPO-inhibitors), glyphosate (Glycines), and mesotrione and tembotrione (HPPD-inhibitors).
What is more alarming, although not unexpected, is that waterhemp has become resistant not only to a single-herbicide-application mechanism, but also “to three or more herbicide mechanisms-of-action.” In other words, even dousing with multiple herbicides is insufficient to keep certain weeds from growing.
Resistance to an herbicide like glyphosate, for example, is already old news. Nebraska has, for a while, been witnessing incidents of glyphosate resistant waterhemp. Other weeds showing resistance to glyphosate in Nebraska include marestail, giant ragweed and kochia.
And it’s not just Nebraska that is seeing herbicide resistant waterhemp. This year, three other states — North Dakota, Iowa and Oklahoma — reported herbicide resistant waterhemp.
North Dakota reported waterhemp resistance in fields of genetically engineered glyphosate resistant sugarbeets and soybeans.
In Oklahoma, waterhemp resistance has become an “even greater concern” with some populations being able to survive up to 8 times the normal dose of glyphosate. “Many other states,” notes the Oklahoma Extension News, “including Arkansas, Mississippi, Kansas, Minnesota, Iowa, Illinois and Missouri, have also documented cases of glyphosate-resistant waterhemp.” The Oklahoma Extension News reminds farmers that:
Glyphosate-resistant waterhemp, like all herbicide-resistant weeds, developed from the over-use and over-reliance on glyphosate. (emphasis in the original)
Iowa State University is equally concerned with glyphosate resistant waterhemp. “[T]he selection of herbicide resistant waterhemp biotypes … threatens to return us to an era where uncontrolled waterhemp causes significant yield losses across the Cornbelt.” The waterhemp resistance in Iowa is disconcerting because, unlike in other states where over-reliance on a single herbicide was cited as the root cause of waterhemp resistance, in Iowa, farmers followed the recommendation to use different herbicides to prevent resistance and yet it still developed.
Bill Freese, the Science Policy Analyst at the Center for Food Safety, in an email to GMO Journal, commented:
As the finding in Nebraska and other research shows, this [pesticide treadmill] approach is not only toxic but futile. Already resistant weeds will readily evolve resistance to 2,4-D as well. Even now, multiple herbicide-resistant weeds are spreading rapidly, and sure enough, industry is developing multiple-herbicide resistant crops in response. Ultimately, this vicious circle of increasing resistance in weeds and crops, and rising use of multiple herbicides, benefits only the pesticide-seed industry (largely one and the same). Only a renewed commitment to non-chemical weed control methods like cover crops can break this vicious circle.
The University of Nebraska-Lincoln researchers who reported on the problem made a similar point when they stated:
New technologies that confer resistance to 2,4-D and dicamba (both synthetic auxins) are being developed to provide additional herbicide options for postemergence weed control in soybean and cotton. The development of 2,4-D resistant waterhemp in this field is a reminder and a caution that these new technologies, if used as the primary tool to manage weeds already resistant to other herbicides such as glyphosate, atrazine or ALS-inhibitors, will eventually result in new herbicide resistant populations evolving. This will limit the value of those technologies to farmers.
Dow AgroScience LLC has filed a petition with the Animal and Plant Health Inspection Service of USDA to deregulate 2,4-D resistant corn. The public comment period will expire on February 27, 2012.