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Impacts of GMO Crops

Impacts of GMO Crops

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Annual Spray Days


Herbicides are the only type of pesticide for which use is rising in the U.S. and worldwide, with no end in sight. Why?

Because of the widespread adoption of genetically-engineered crops (also known as GMOs), and the spread in their wake of herbicide-resistant weeds.

GMO corn, soybeans, and cotton engineered to resist post-emergent (during the growing season) applications of herbicides including glyphosate (e.g. Roundup), 2,4-D, and dicamba are the fuel pushing the herbicide treadmill into ever-higher gears.

Before herbicide-resistant GMO crops, farmers could only spray fields with broad-spectrum herbicides at the beginning of the year to kill weeds before planting, or after the crop was harvested.

Broad-spectrum herbicides are Roundup capable of killing a wide range of plants, including both weeds and agronomic crops, leading to limits on when such herbicides can be applied. GMO technology extends by several weeks to a few months the time period during which broad-spectrum herbicides can be sprayed on actively growing crops, killing weeds but leaving the farmer’s cash crop unharmed.

Herbicide use across the Midwest has increased dramatically in the last decade as a result of the spread of dozens of weeds resistant to multiple herbicides.

Excessive reliance on just one herbicide – glyphosate – has triggered the emergence and spread of over a dozen glyphosate-resistant weeds. This has, in turn, forced farmers to spray additional herbicides, often at higher rates and, in many fields, more than once in a season.


In addition to the worsening weed management challenges across the Midwest, corn-soybean farming system changes have led to:

  • The widespread coating of seeds with multiple fungicide and insecticide seed treatments;
  • A troubling rise in fungicide spray applications on corn; and
  • Spread of insects resistant to the Bt toxins produced by GE-Bt corn, coupled with insecticide applications to forestall the spread of Bt-resistance insects.

Click here for more on the impacts of GMO crops on pesticide use.

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