Crops do not damage the environment simply because they are GM. Some farming practices, such as the overuse of herbicides resulting in the excessive eradication of wild plants from farmland have been shown to harm the environment. These problems are similar for non-GM and GM crops.
In a large farm scale evaluation of herbicide tolerant GM crops conducted in the UK between 1999 and 2006 it was shown that when weed control is particularly effective insect biodiversity is reduced. It did not matter whether or not the crop was GM- the important factor was how many weeds remained in the crop. Damage to wildlife can be reduced if a small amount of agricultural land is set aside for biodiversity.
A related issue is the growing problem of weeds becoming resistant to herbicides, due to the overuse of those herbicides. Herbicide tolerant crops, whether GM or non-GM, can cause this problem because repeated growth of the same herbicide tolerant crop involves repeated use of the same herbicide. One solution is the rotation of crops resistant to different herbicides, or rotation of herbicide use with use of other weed control strategies.
The use of GM crops resistant to insects through introduction of the gene for Bt toxin has environmental benefits. For example GM insect resistant cotton has substantially reduced the application of more environmentally damaging insecticides, with consequent environmental benefits and health benefits for cotton farmers.
Damage to wildlife can be reduced if a small amount of agricultural land is set aside for biodiversity.
However, just like herbicide resistant weeds, insect pests can develop resistance to insecticides whether they are produced in the crop itself by GM, or sprayed onto the crop. This problem is less frequent if a rotation of different insect control procedures is used.
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