Genetically engineered or modified crops were supposed to herald in a new green revolution with reducing use of pesticides and better crop production. A recent study onto the first 16 years of use of GM crops has shown that pesticide use has soared as herbicide resistant weeds take hold.
As any ecologist will tell you the natural world is a battle ground with chemicals weapons being used to fight off the competition. So it should come as no surprise that weeds would eventually become resistant to herbicides resulting in the need for ever more herbicides to be applied and the need for newer herbicides to be developed.
A study by Washington State University research professor Charles Benbrook used official data from the U.S. Department of Agriculture’s National Agriculture Statistics Service to see how pesticide use has changed during the 16 year commercial history of GM crops. [pullquote]Resistant weeds have become a major problem for many farmers reliant on GE crops, and are now driving up the volume of herbicide needed each year by about 25 percent,[/pullquote]
He examined 6 different types of GM crops – 3 were resistant to herbicides – glyphosate resistant corn, cotton and soybeans - and three were insect resistant Bt varieties - 2 x Bt Corn and a Bt Cotton.
What he found was that over the 16 year period of glyphosate resistant crops there was an increase in glyphosate herbicides of 17% over the period as weeds become evermore resistant to the herbicide.
The Bt corn and Bt cotton did have a more positive impact with a reduction in the use of insecticides against the three targeted pests – European corn borer, corn rootworms and cotton Lepidopteron insects. However there is now evidence that corn rootworms are becoming resistant to the toxins that are produced by the GM corn and growers are again being advised to start soil insecticide treatments in resistant affected areas.
Professor Benbrook discovered that during the study period while the use of insecticide in the US fell by 56 million kilogrammes the use of the glyphosate herbicide rose by 239 million kilogrammes this resulted in a combine extra use of pesticides of 183 million kilogrammes or 7% during the commercial history of GM crops. If the resistant corn rootworm populations expand then insecticide use will start to increase again.
“Resistant weeds have become a major problem for many farmers reliant on GE crops, and are now driving up the volume of herbicide needed each year by about 25 percent,” Benbrook said.
“The annual increase in the herbicides required to deal with tougher-to-control weeds on cropland planted to GE cultivars has grown from 1.5 million pounds in 1999 to about 90 million pounds in 2011.”
The study shows that GM crops worked well in the first few years but soon those benefits were lost as the resistant weeds took hold requiring farmers to spray more often and in larger quantities as well as adding new herbicide types in to their spraying routine.
The study highlights the fear that if new herbicide resistant crops are licensed then the use of herbicides will soar. One of the new breed of GM crops due to be licensed is resistant to 2,4-D. If this GM crop is approved there are fears that herbicide use will increase by another 50% as resistant weeds evolve.
Environmental Sciences Europe: Impacts of genetically engineered crops on pesticide use in the U.S. — the first sixteen years.