Genetically modified (GM) crops are altered in a number of ways that change their behaviour in the environment. They may have genes added so the crop is no longer killed by chemical weedkillers (herbicides) so farmers can spray the chemicals and kill the weeds but not the crop. Or genes may be added which produce a toxin so that insects feeding on the crop are killed.
GM crops are living, able to grow and multiply. There are concerns that GM crops will end up in wild plants or in non-GM crops. There are also concerns that altered farming practices used to grow these crops will affect the environment.
Scientists have highlighted the kinds of effects growing GM crops may have on the environment:
- Other crops and wild plants may become contaminated with the foreign genes added to the GM crop.
- New 'super-weeds' may evolve which will be difficult or even impossible to eradicate.
- Pollution arising from the use of harmful chemicals may increase or decrease.
- Wildlife may be harmed by new toxins in the environment or changes in agricultural practices.
Genetic contamination: Crops were developed by farmers over thousands of years from plants that were once wild. Many crops have wild relatives growing close by that they can cross-pollinate. In Britain, it is sugar beet and oilseed rape - two of the GM crops that may be grown here first - that have wild relatives which could be contaminated. In tropical countries, where most crops evolved, there is a greater potential for genetic contamination. Already, GM maize imported into Mexico has contaminated native varieties.
Crops grown by organic and non-GM farmers may also be affected. Pollen can travel long distances on the wind or via insects. Separating GM from non-GM fields may help reduce contamination, but farmers and consumers could be forced to accept contamination if GM crops are grown here. Seed mixing can also occur accidentally on the farm or in the supply chain.
Super-weeds: One potential outcome of growing GM crops is that they may become problems themselves as happens when some exotic species are introduced into a new country. In the UK, the introduction of grey squirrels and rhododendrons have caused considerable environmental damage, some of which may never be put right. In Canada, where GM oilseed rape is grown, super-weeds that are resistant to three herbicides are a problem for farmers. GM oilseed rape has pollinated other rape and the seed left in the field after harvest grows as a weed in the next crop. Farmers are turning to more toxic chemicals such as 2,4 D and paraquat to control them. Superweeds are now spreading in the US and South America as a result of the use of large applications of weedkillers on herbicide-tolerant GM crops.
Pollution: The biotechnology industry has claimed that GM crops will allow farmers to use less chemical weedkillers and insecticides. The majority of GM crops being grown worldwide are tolerant to Monsanto's weedkiller, Roundup, or Bayer's weedkiller, Liberty. The companies making the chemicals also sell the GM seed. However, in North America - where GM soybean, cotton and maize are grown on thousands of acres - the use of weedkillers has not been reduced. Sales of Roundup and Liberty have increased and new factories are being built to make more.
The companies argue that Roundup (glyphosate) and Liberty (glufosinate) are less damaging to the environment than other chemicals even though they kill almost all green plants they contact. However, sometimes GM Liberty tolerant maize has not performed well and the old chemicals, such as atrazine, have been reintroduced to control weeds.
The only case where chemical use has been reduced is GM cotton with an inbuilt insecticide called Bt. Conventional cotton production often involves many - often 8 or 9 - applications of insecticide and Bt cotton has reduced this. However, the reduction may be short lived as many farmers are not following plans to prevent insects developing resistance to Bt. In some cases, there has been an explosion of new pests that are not affected by the Bt toxin. Furthermore, some varieties of Bt cotton have been removed from sale in India due to their poor performance.
Wildlife: The gradual disappearance of birds from our farmland has shown us how agricultural practices can harm wildlife. The UK's farm-scale evaluation with two of the first GM crops that could be grown here, herbicide tolerant oilseed rape and sugar beet, showed that their use would be likely to lead to further declines in farmland wildlife.
- GeneWatch briefings
- Press articles
- The Guardian: Tracking the causes of monarch butterfly decline (18th April 2013)
- Independent: On a wing and without a prayer - the decline of the monarch butterfly (17th March 2013)
- Star Tribune: Study ties GMO corn, soybeans to butterfly losses (16th March 2012)
- UPI: Resistant weeds said threat to U.S. crops (4th February 2013)
- Farm Industry News: Glyphosate-resistant weed problem extends to more species, more farms (29th January 2013)
- The Western Producer: Scientist raises concerns about GM crops and glyphosate (21st December 2012)
- New York Times: Pesticides: Now More Than Ever (11th December 2012)
- Bloomberg: DuPont-Dow Corn Defeated by Armyworms in Florida: Study (16th November 2012)
- Bloomberg: Bugs Damaging Monsanto Corn May Do Same to Syngenta Crops (14th November 2012)
- Guardian: How GMOs unleashed a pesticide gusher (3rd October 2012)
- Reuters: Pesticide use ramping up as GMO crop technology backfires: study (1st October 2012)
- Deccan Chronicle: Bt cotton toxic, bollworms seek new hosts (23rd June 2012)
- BBC News: GM crops 'aid plant neighbours' (14th June 2012)
- Nature: War on weeds loses ground (22nd May 2012)
- Daily News Tanzania: Superweeds caused by GMO are super problems (20th May 2012)
- Huffington Post: Bee Kills in the Corn Belt: What's GE Got to Do With It? (16th May 2012)
- Superweeds: A Long-Predicted Problem for GM Crops Has Arrived (15th May 2012)
- Reuters: Super weeds no easy fix for US agriculture-experts (10th May 2012)
- San Francisco Chronicle: Genetically modified crops' results raise concern (30th April 2012)
- New York Times: A Battle Over an Engineered Crop (25th April 2012)
- Reuters: Analysis - Dow's new corn - "time bomb" or farmers' dream?
- International Business Times: Monsanto Bt Crops: Genetically Modified Corn Linked To Soil Ecosystem Threat (17th April 2012)
- Summit Voice: Popular weedkiller causes deformities in amphibians (3rd April 2012)
- Reuters: Analysis: Food security focus fuels new worries over crop chemicals (27th March 2012)
- Daily News (Tanzania): GMO varieties could harm wild relatives (25th March 2011)
- Western Farm Press: EPA urged to address rootworm resistance to Bt corn (23rd March 2012)
- StarTribune: Study ties GMO corn, soybeans to butterfly losses (16th March 2012)
- Reuters: Scientists warn EPA on Monsanto corn rootworm (9th March 2012)
- Science Daily: Lethal Effects of Genetically Modified Bt Toxin Confirmed On Young Ladybird Larvae (27th February 2012)
- Penn State Live: Integrated weed management best response to herbicide resistance (9th February 2012)
- Bloomberg: Monsanto Says Weedkiller-Resistant Kochia Found in Western Canadian Fields (12th January 2012)
- Daily Mail: Super weeds 'run rampant in fields near GM crops', scientists warn (21st October 2011)
- The Guardian: GM crops promote superweeds, food insecurity and pesticides, say NGOs (19th October 2011)
- ArabNews.com: Super weeds pose growing threat to US crops (19th September 2011)
- Wallaces Farmer (USA): Glyphosate-Resistant Weeds Are Huge Challenge (9th August 2011)
- St Louis Today: Resistant weeds leave farmers desperate (17th July 2011)
- External links
Increased mortality is predicted of Inachis io larvae caused by Bt-maize pollen in European farmland
Predicts that butterlies may be harmed by the Bt toxins produced by GM pest-resistant maize in areas of central and southern Europe where butterflies breed twice a year.
- Benbrook C (2012) Impacts of genetically engineered crops on pesticide use in the U.S. - the first sixteen years
- Increased mortality is predicted of Inachis io larvae caused by Bt-maize pollen in European farmland