Cotton (Gossypium hirsutum L.) has been genetically modified to be resistant to herbicides with an active substance such as: glyphosate, glufosinate, dicamba and 2,4-D. Combinations with inserted genes for resistance to two of these herbicide tolerance traits are widespread. Almost 100% of all cotton from the United States has been genetically modified to be tolerant to one or more types of herbicides based on these four active substances. The use of herbicides on cotton has therefore increased and is increasing because weeds have developed resistance to glyphosate. Genetically modified for 2,4-D resistance is now included in the development of herbicide-resistant cotton. GMO cotton is now being inserted with several genes for resistance to the several different herbicides used against resistant weeds.
Cotton with 2,4-D resistance is due to the insertion of the aad-12 gene from a bacterium (Delftia acidovarans) to produce the AAD-12 enzyme (aryloxyalkanoate di-oxygenase 12). This enzyme catalyzes the breakdown of 2,4-D herbicide. It is cotton that has now been genetically modified for tolerance to the three different active substances glyphosate, glufosinate and 2,4-D. This means that different types of herbicides with a total of three different types of active ingredient can be used. This can form the basis for a collapse in ecosystems near and far. It can damage ecosystems in soil, streams and water.
Glyphosate can cause a shift in the composition of microflora in the soil and in the gut in different ways. Glyphosate, for example, can lead to an increased proportion of pathogens such as Fusarium fungi in soil, and increased Salmonella and Clostridium in the digestive system of poultry. Glyphosate can alter ecosystems in an undesirable way. It can also create a toxic environment in fresh water. Glyphosate can cause widespread irreversible ecotoxicity. Glufosinate can reduce predatory insects and butterflies. Glufosinate ammonium has the potential to induce severe reproductive and developmental toxicity in rodents.
In most types of GMO cotton, the herbicide-resistant crops also often have a gene for insect resistance inserted. This increases the ripple effects it can have on the environment. Cotton has a Bt gene inserted to form Cry-toxin against moth larvae. This forms a large biomass containing insecticides. Moth larvae have developed resistance to Cry toxin in many places. Cotton seeds with several (2-3) different genes are therefore sold and bought to form several different varieties with toxins. This is to prevent the development of resistance in moth larvae which will damage the cotton crops. These seeds cost several times more than ordinary cotton seeds.
In India, moth larvae are also a primary problem on cotton. This problem is controlled with GMO crops inserted Cry protein (insecticide). These toxins have been chosen because they are most toxic to moth larvae that eat cotton bolls and destroy crop yields. These formed the primary insect problem in many places where cotton will be grown. Where this problem is gone, secondary pests are the problem. Woolly scale lice, aphids and thrips are all pests that can rule GMO cotton. This increases the likelihood of invasion of the pests by other new resistant pests.
Using all GMO agents against resistant insects and weeds at the same time can be very expensive. Both more expensive seeds and more consumption of more pesticides will cost much more. Combinations with multiple genetic modifications for super resistance to pesticides and insects increase the height of the fall for buyers. It is a risk that creates many losers. It is the small farms that are most often ruined. They have nothing left to sell.
Schütte G., Eckerstorfer M., Rastelli V., Reichenbecher W., Restrepo-Vassalli S., Ruohonen-Lehto M., Wuest-Saucy AG, and M. Mertens. 2017. Herbicide resistance and biodiversity: agronomic and environmental aspects of genetically modified herbicide-resistant plants. Environmental Sciences Europe 19:5.