Fears that growing genetically modified herbicide tolerant (GMHT) oilseed rape and sugar beet will create uncontrollable super-weeds are unfounded, recent research suggests.

Indeed, herbicide-tolerant beet could offer a fresh start in the weed beet battle.

However, some management practices would need to change, the study by Rothamsted Research and ADAS concludes.

"GMHT beet would give us a superb opportunity to get rid of the weed beet problem and start again," says one of the authors, Broom's Barn's Mike May.

Conventional weed beet plants would be killed by the spray used in the HT crop, for example, glyphosate, removing the reservoir that plagues many farms at a stroke.

"With a bit of effort we could stop the problem building again," says Mr May. Modern varieties are much less susceptible to bolting, though some control will still be needed.

"With herbicide tolerant beet it is vital to remove any bolters from the crop before they flower and release pollen, otherwise gene flow to weed beet will occur, so creating herbicide tolerant weed beet," he explains.

Tolerant

Wiping with glyphosate would no longer be an option if the GM crop was tolerant to that herbicide.

"Cutting and hoeing would still be appropriate, but would have to be done earlier and more often than normal."

With oilseed rape, provided the anticipated isolation distances between crops were enforced, the transfer of herbicide tolerance to adjacent crops would be low, though it would be sensible to keep monitoring the picture, the report suggests.

The main problem with GMHT crops appears to be determining how long to leave between sowing a non-herbicide tolerant crop after growing a GMHT one.

Oilseed rape volunteers from shed seed could exist for up to 10 years. That could have implications for growers wishing to follow with a non-GM crop in that period and stay within the 0.9% admixture threshold.

Harvesting at the right time to minimise seed losses and not cultivating for at least 20 days after cutting should help minimise subsequent problems, advises Rothamsted's Peter Lutman.

Tackling

Some set-aside practices might be affected - for example glyphosate-tolerant volunteers would need tackling with another active, say metsulfuron, explains Dr Lutman.

The main impact would be on subsequent cropping with linseed, sugar beet and beans where some types of tolerance would reduce the herbicide armoury available in those crops.

Commenting on the findings, the Advisory Committee on Releases to the Environment* notes that any changes in herbicide practice would remain within the bounds of good agricultural practice.

However because controlling GMHT volunteers would be easier in winter wheat than in spring crops, farmers might prefer to grow those instead.

That would mean losing over-wintered stubbles which has been linked to the decline in plant, insect and bird populations over the past few decades, says ACRE.

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