ENVIRONMENTAL IMPACT OF GM HERBICIDE-TOLERANT CROPS: THE UK FARM SCALE EVALUATIONS AND PROPOSAL FOR MITIGATION

In October this year, the long-awaited results of the UK Farmscale Evaluations (FSE) of the environmental impact of GM herbicide-tolerant (GMHT) crops were published in the prestigious journal, Philosophical Transactions of the Royal Society. In the ensuing media frenzy, the headlines suggested that beet and springsown oilseed rape (canola) were harmful and maize less harmful to the environment compared to their conventional equivalents. To the environmentalist, the label ‘harmful’ is based on the premise that fewer weeds lead to fewer weed seeds, the decline of which would provide less food for birds and other wildlife within the crops, and less seed return to the seedbank. To the farmers, the initial outcome of this could be described as beneficial. In essence the study concluded that the already depleted arable ecosystem (compared to an undisturbed environment) would be further depleted by the use of GMHT technology because these ’break crops’ are regarded as having a restorative function for the seed bank in a normal rotation. That is, weed control within conventional varieties of beet and oilseed rape is relatively poor, and this allows the in-field plant species to replenish their seed stocks with consequent benefits for the dependent food chain. Environmental organizations such as English Nature and the Royal Society for the Protection of Birds (RSPB) raised major concerns about the long-term impact of these GMHT crops on wildlife in general, and birds in particular. These concerns were raised against the background of declining populations of both weed seeds, especially of broad-leaved plants (circa 3% per annum) and several species of farmland birds (up to 60% decline in some species since 1970), though other species have shown no decline or even gain. Effects on Plants To some extent, the results of the FSE reinforce these concerns. As used in the trials, the herbicides applied to GMHT beet(glyphosate: Roundup Biactive from Monsanto) and spring sown oilseed rape (glufosinate ammonium: Liberty from Bayer CropScience) did give better weed control than the conventional herbicides used on the non-GM crops, and this did lead to lower weed biomass at the end of the season, and fewer weed seeds being caught in seed rain traps. There were also fewer seeds in the seed bank in the following year in the next crop (mostly cereals) in the rotation 1,2 . In maize the opposite was true. Glufosinate applied to the GM variety gave poorer control of weeds than the conventional regimes, which, in 75% of the test crops, were based on atrazine applied mostly pre-emergence. As atrazine is a persistent, relatively broad spectrum residual herbicide, it is not surprising that it gave better control than one that was applied some time after the crop and weeds had emerged. Indeed, conventional maize crops had the fewest weeds, lowest weed biomass, and produced fewest weed seeds of all the crops tested. The recent announcement within the European Union that atrazine would be banned in the near future has cast doubt on the validity of the maize results; however, as this intention was not known at the time the experiment was devised, the results remain valid for the comparisons that were made. Further work may need to be done to re-examine the comparison when farmers have selected alternative conventional products in a couple years time, after the ban has been implemented. Effects on Invertebrates