14 November 1997

GM rape not a tricky weed

By Andrew Blake

TRANSGENIC herbicide resistant oilseed rape is unlikely to be any more troublesome as a weed than its conventional cousin, according to early NIAB work.

Three years monitoring of sites used for trialling varieties genetically modified (GM) to tolerate broad spectrum weed-killers confirms earlier small-scale studies, says Jeremy Sweet.

Cross pollination, seed dispersal and competitiveness, all areas of potential concern, were examined in detail at six sites and in further field margin trials.

"Our conclusion is that there is no indication that either winter or spring modified rape is especially aggressive," says Dr Sweet.

Volunteers of GM rape were generally low in following crops. This suggests they are as well controlled by current farm practices as their conventional counterparts. Specific problems can be linked to a missed sprayer strip at one site and seed spillage during harvest at another, he adds.

At Cambridge, where roughly equal areas of both types of winter rape were trialled in 1995 in the first big release of GM varieties, 77 volunteers were found in the 5ha (13 acres) of following winter wheat. "We would have expected half to be transgenic," says Dr Sweet. "In fact only five were."

To date no cross-pollination which might transfer the GM herbicide tolerance to nearby oilseed rape crops or related weeds has been detected in several thousand seed samples, he reports. But tests are continuing.

Introducing GM rape will inevitably alter weed-killing programmes which could have a knock-on effect on the environment, says Dr Sweet. "The agricultural effects could be significant if we are going to start using more broad spectrum herbicides. We need to look carefully at what we are doing."

Hedges and field margins, which harbour beneficial insects and other wildlife, could be more at risk. "In addition are we opening up the areas in the field margins for larger populations of volunteer rape to establish?"

New MAFF-funded work is examining the potential threats from spray drift into such areas.

The latest experiments involved broadcasting both conventional and GM rape into field margin plots subjected to various herbicide treatments including glufosinate and glyphosate.

In practice pigeons and slugs meant few oilseed rape plants of either type established in the cleared areas. "But there is no indication that the transgenic rape is any fitter than the normal."

Despite the NIAB findings, managing farms with transgenic crops is bound to become more complicated, warns Dr Sweet. "The more herbicide tolerant crops you have in the rotation the more complex the management will become." &#42

Left:Herbicide resistant GMrape volunteers in a field margin sprayed with a broad spectrum herbicide. NIAB is investigating whether these herbicides will do more damage and encourage more rape volunteers to establish. Right: GMrape volunteers in a crop of sugar beet. Will such GMvolunteers become problem weeds in other GM crops?

TRANSGENIC RAPE

&#8226 Three years monitoring.

&#8226 Volunteer levels as normal.

&#8226 No cross-pollination to weeds.

&#8226 Margin work inconclusive.

&#8226 Management more complicated.