Their verdict comes as the Mali government decides whether to allow trials of genetically modified crops to begin in the country.

During the five-day meeting in Sikasso, in the south of Mali, where two thirds of the country's cotton is produced, farmers heard arguments for and against the introduction of GM technology.

Biotechnology scientists claim to be able to produce an insect-repellent cotton crop that would survive attacks by bollworm, a pest that has destroyed large swaths of the country's crop in recent years.

But environmentalists argue that the benefits of genetically modified crops are outweighed by the harm done to local farmers. "GM technology gives seed companies power over the entire agricultural sector," said Dr Michel Pimbert, director of the London-based International Institute for Environment and Development, which organised the meeting. He added: "Crops are protected by patents, so farmers are unable to keep the seeds from the harvest and re-sow them the next year as they do at the moment. The idea that the first link in the agricultural link is controlled by a company is deeply disturbing to small farmers."

Farmers at the meeting said they needed help to continue their existing farming practices, and worried that new GM technology would damage their way of life. Birama Kone, a smallholder on the jury, said: "GM crops are associated with the kind of farming that marginalises the mutual help and co-operation among farmers and our social and cultural life."

The development of GM technology in west Africa is backed by USAid, the American development agency, but activists point out that Mali's cotton industry would thrive if the United States stopped subsidising its own 25,000 cotton farmers by $3bn (£1.7bn) a year. West African countries were hit hard by falling world cotton prices in the 1990s, and have complained that the American cotton subsidies are driving them out of business. A report by Oxfam argues that the US cotton subsidies cost most west African cotton-producing countries the same amount in lost export earnings that they receive in American aid each year.

The farmers' rejection of GM technology at the Sikasso meeting is not legally binding, but the farmers hope the government will take their views into account when making a decision about the future of GM crops in the country.

African countries have been wary of accepting GM technology, despite assurances from the US government and biotech companies that the products are safe. In 2002, Zambia refused to accept genetically modified relief food despite the threat of famine. Zimbabwe, Malawi, Mozambique, Lesotho and Angola later said they would only accept maize if the seeds were milled into flour, to prevent cross-pollination with local maize crops.

Only a handful of countries, including South Africa and Burkina Faso, have allowed GM crops into their farming sector. In Mali, the cotton industry accounts for half of export earnings.

Mourad Abdennadher, west Africa regulatory manager for Monsanto, one of the main biotech companies, said Mali did not have the legal framework to cope with GM technology. "We cannot go into a country unless there are clear biotech regulations, covering matters of bio safety, and of how trials should be conducted and presented. Mali has none of these," he said.