The environmental group, Genetic Concern, has disputed claims by biotech companies that GM crops lead to increased yields and less pesticide use.
Its spokeswoman, Ms Sadhbh O'Neill, accused Monsanto in particular of "distorting the reality which many US farmers are experiencing with GM crops".
However Monsanto insists, for example, its GM sugar beet trials in Ireland have already "indicated the potential to achieve in Ireland reductions of up to 40 per cent in pesticide usage and enhanced root vigour of at least 10 per cent" compared to conventional crops.
Its Irish business manager, Dr Patrick O'Reilly, says these figures mirror test findings elsewhere and could provide financial savings and increased income for producers. Monsanto is outlining the midway results of its five-year trial to farmer representatives and the agricultural press this week.
Analysis of data from the US department of agriculture (USDA) on the benefits of GM crops by Dr Jane Rissler of the Union of Concerned Scientists "shows that far from delivering higher yields and reduced herbicide usage, farmers in the US have experienced mixed results", Ms O'Neill claimed.
In the majority of crops and regions surveyed, there were no statistically significant differences in pesticide use or yield between engineered and non-engineered species, she said. This contrasts with strong evidence from many US farmer groups that they are generally using less pesticide with GM crops.
e and Dr Britt Bailey of the Centre of Ethics and Toxics in California had also outlined a study in their book Against the Grain showing that for 30 out of 38 varieties grown in the US, the conventional soyabean outperformed the transgenic version.
A Monsanto spokesman said the USDA figures had been misinterpreted in a number of recent publications. The data had indicated both reductions in pesticide use and yield increases from GM crops. Moreover, the findings had been corroborated by other independent studies, which showed a marked decrease in chemical pesticide usage across a variety of crops. "We totally reject this claim. In our view it goes against all available evidence indicated by independent experts and our trials in Ireland. It's yet another attempt by the opponents of GM foods to distort the truth," he said.
Genetic Concern also claimed GM crop tests were failing to investigate the long-term impact of replacing specific herbicides with a "broad spectrum herbicide" such as glyphosate, which goes under the Round-Up trade name.
