In 2004, farmers in Georgia discovered a weed that was resistant to glyphosate, the active ingredient in Monsantoโs Round Up herbicide. The weed, palmer amaranth, quickly became the โposter child for the potentially devastating impacts of herbicide-resistant weeds,โ writes Andrew Kniss, Associate Professor of weed biology and ecology at the University of Wyoming. National news outlets immediately coined the term โsuperweed,โ and some said it threatened the sustainability of cotton production in the southeastern US.
However, Kniss writes, according to the US Department of Agricultureโs National Agriculture Statistics Service, the average cotton yields since 1938 have increased by an average of 7.9 lbs/acre/year. Since 2004, when โsuperweedsโ were discovered, national cotton yields have actually been higher than the long-term trend. The same trend was found in Georgia, Arkansas and North Carolina, where palmer amaranth has been said to be devastating farmersโ fields.
Farmers have had to use additional weed-control methods, such as tillage, cover crops and other herbicides to fight the โsuperweeds,โ Kniss writes, which may contribute to their reduced net economic gains. But โit is important to note that these herbicide-resistant weeds have not had the devastating effects on crop yieldsโฆthat is often implied by the sensational coverage of this topic.โ
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