BioEd Online

British crop researchers are claiming that they have developed a method to stop transgenic crops from damaging the biodiversity of weeds and seeds. By leaving two rows in every 100 unsprayed with pesticides, enough diversity can be preserved to prevent knock-on effects on birds and other animals, they calculate.

The method could help farmers to reap the economic benefits of planting herbicide-resistant crops while avoiding the environmental damage of blanket pesticide spraying, say researchers led by John Pidgeon of Broom's Barn Research Station in Bury St Edmunds, UK.

Farmers typically spray pesticide on their crops using a multi-jet boom sprayer up to 24 metres wide. "All they would have to do is turn off the outside two nozzles," says Pidgeon.

This reduction would allow weeds to produce seeds in the unsprayed rows, preserving plant diversity and giving birds and insects a source of food, Pidgeon and his colleagues say in a paper published online by Proceedings of the Royal Society B¹.

Obvious idea

The researchers undertook their work after the UK government's Farm Scale Evaluations (FSE) reported in 2003 that herbicide-tolerant sugar beet and oilseed rape can damage biodiversity because of the vigorous pesticide regimes used to manage these crops.

Pidgeon is surprised that the idea of leaving some rows unsprayed has never been evaluated before. "It occurred to me about four seconds after the [FSE] results were published — it is desperately obvious," he says.

They haven't yet tested the idea of leaving small strips of cropland untouched by pesticide. Instead, they extrapolated from the FSE experimental results for sprayed and unsprayed fields to see how much needed to be left alone to encourage biodiversity. Leaving 2% of the crop untouched should allow weed seeds to grow; leaving 4% unsprayed allows weed plants to flourish, they predict.

Although genetically-modified herbicide-tolerant (GMHT) crops are grown throughout the United States, they will not be approved in Europe unless seed producers such as the US giant Monsanto can show that their strains will not harm the environment any more than conventional ones do. This makes it surprising that they have not yet tested the beneficial effects of leaving rows unsprayed, says Pidgeon's co-author Joe Perry.

Such a proof of principle could be carried out in just one growing season and could even be done with non-genetically-modified test strains, he adds.

Win-win?

Whether the practice can be enforced, however, remains unclear. "Will farmers do it, and how do you tell they have really done it?" asks Matthew Heard, an ecologist at the Centre for Ecology and Hydrology in Huntingdon, UK. "Farmers just want to maximize yields." Losing some of the unsprayed 2% to weeds might not seem to them like a good deal.

Pidgeon claims that his technique will allow farmers to boost their profits — GMHT sugar beet is thought to be worth an extra £150 ($299) per hectare than conventional varieties — and completely avoids the damage to weed and seed diversity. "If you leave 2% unsprayed, GMHT sugar beet is actually better for the environment [than normal sugar beet]," he says. "It's a win-win: economically and environmentally."

Nevertheless, "there are weeds and there are weeds", warns Les Firbank, a researcher at the Institute of Grassland and Environmental Research in Okehampton, UK. Some pests, such as black grass, are devastating to crop yields while not really providing much benefit to wildlife. Farmers would much prefer to find subtle ways to encourage broadleaved weeds.

Heard argues that restoring British biodiversity will take more than the "gimmicky" idea of leaving rows untreated with pesticide. Decades of intensive agriculture have already damaged wildlife; farmers should be trying to fix this previous damage by leaving wider margins around their fields, he says. "What we want to do is reverse these disastrous historical impacts," he says.