GMHT principle is weapon not a total answer

28 November 1997

GMHT principle is weapon not a total answer

GENETICALLY-modified herbicide tolerant crops could simplify weed control and boost yields. But North American experience so far is not all favourable and suggest cost savings may not be the key benefit.

Surveys by Monsanto and AgrEvo show a high level of user satisfaction and a continuing upsurge in the planted area. But independent observations from Iowa State University show the switch to GMHT crops is not simple and does not cure all weed problems.

"Herbicide tolerant GM crops are tools to fight weeds, not answers in themselves," says Dr Mike Owen of Iowa State University, USA. "Farmers consider it to be simple and fool-proof for all weed control problems. We would suggest those assumptions are naive."

Headaches he identifies include wrong application timings and rates, a lack of residual activity and the danger of contractors treating the wrong crops.

"Timing and rates are incredibly important." With no residual activity timing must be spot on to remove weeds when most have emerged, but before they are competing with crops vigorously. In some cases the problem is compounded by growers using stubble cleaning rates, which fail to perform in the cropping situation.

Local conditions mean target rates and timings may not always be the same as those recommended by the manufacturer, he notes.

But a survey of US Round-up Ready soya bean growers this year showed 81% were very satisfied with their results, says Steve Moll, Monsantos project leader for GMHT crops in Europe.

Furthermore, 70% said weed control was better than with conventional chemistry. However, that did not seem to translate into a more economic result.

When asked what the key benefit of the technology was 42% said good or better weed control, while just 13% reckoned it was a more economic approach.

In 1996 the average yield benefit from growing GMHT Round-up Ready soya was 4.8%, accompanied by a 9-39% reduction in the amount of herbicide used, Mr Moll adds. Plantings of GMHT soya are set to rise again next year, taking over 30% of plantings, Monsanto forecasts.

Growers of Roundup Ready Canola rape reckoned they had a 9% yield response, with a typical Can$50-60/ha (£ 6-7/acre) cost saving. Sugar beet trials in Europe show an average 3-5% yield boost, thanks to less spray damage to the crop and better weed control from a dual application strategy, he says.

In Canada Liberty Link Canola has impressed growers, with 92% saying germination was better than under conventional systems, notes Ernest Rasche of AgrEvo Europe. "Better weed control allows no-till sowing, which conserves moisture, so giving better establishment."

Yield rose 0.2t/ha and more even maturity in the absence of weeds improved oilseed quality, putting 85% of the crop into the top oil grade, compared with 63% from conventional systems, he says.

Of the users surveyed 43% said they would not have grown Canola on the fields chosen without herbicide tolerance. "Those fields were just too weedy to grow the crop any other way."

Although all North American growers who used Liberty Link maize this year said they would do so again next year, just 9% put cost efficiency as its most appealing feature.


&#8226 Not total weed solution.

&#8226 Rates and timings critical.

&#8226 Treating right crop crucial.

&#8226 Cost/benefit query.

&#8226 North American output soaring.

Farmers must adapt

Farmers wont benefit financially from genetically modified crop technology. But they will have to adopt it to remain competitive in world markets. That is the view of Steve Moll, Monsantos project leader for GM crops in Europe. "Historically the benefits of technical innovation have always fed through to consumers and they are the ones that will reap any cost savings from this technology," he says. "But farmers need to remain competitive and genetically modified crops will help them do that."

Keeping crops weed free by using varieties which have been gentically modified to tolerate total herbicide sprays could be trickier than growers think, warns Dr Mike Owen of Iowa State University.

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