Opponents of genetic modification say no one can vouch for its safety because long-term testing has never been done. They're further concerned about its effect on the environment. Pollen from the biotech crops could spread in the field, killing beneficial insects like ladybugs or creating superweeds impervious to pesticides.

Genetically engineered micro-organisms (GEMs), designed to prevent frost forming on strawberry or potato plants, are being tested in California, under the auspices of the US Environmental Protection Agency, which wants to be sure that any bacteria or fungi with altered genetic characteristics do not harm insects animals, crosp or humans. Another fear is that such organisms might help plants to evolve into 'super weeds', which could become immune to eradication techniques.