www.checkbiotech.org ; www.raupp.info ; www.czu.cz

Fears that growing genetically modified herbicide tolerant (GMHT) oilseed
rape and sugar beet will create uncontrollable super-weeds are unfounded,
recent research suggests, February 2007.

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.

[www.defra.gov.uk]