Fears of a lack of herbicide choice

5 March 1999

GM crops are not for all, say US weed scientists

NOT all growers around the world are adopting genetically modified crops with equal enthusiasm.

In some parts of the US and South America GM herbicide tolerant soya is grown wall to wall. But in some US states, such as Arkansas, uptake has been surprisingly limited, says University of Arkansas weed scientist Ford Baldwin.

"Growers have been happy with the weed control but disappointed with the varieties." Farmers have also been antagonised by Monsantos arrogance and marketing techniques. "Advertisements have been pitting farmer against farmer, encouraging neighbour to snitch on neighbour."

Technology fees and grower contracts are the root of the problem, forbidding growers to farm save seed and allowing Monsanto access to farm crops whenever they please. "They are like an alligator in the commode." The fact that Argentine competitors do not have to pay technology fees is also considered unjust, leading to 89% of the current Argentine crop being GM.

Uptake is nearly as great in some US states, like North Carolina, where former problem weeds such as sicklepod can now be controlled.

But timing is crucial, and some growers have been disappointed where management of the glyphosate tolerant crops has been lax. "There are several species of weed which, if the timing is wrong, cant be controlled at all. Glyphosate is not a one-shot solution," stresses Dr Baldwin.

Monsanto recommends two treatments with Roundup, the first two weeks after crop emergence to hit the tough weeds while they are small. Other companies recommend one glyphosate-type treatment plus an alternative control, usually a soil applied pre-emergence product.


&#8226 Uptake depends on weed spectrum.

&#8226 Conventional herbicides still needed.

&#8226 Application timing crucial.

&#8226 Weed population shifts likely.

&#8226 Resistance probable long-term.

Fears of a lack of herbicide choice

HERBICIDE tolerant genetically modified crops are already prompting fears of a decline in the availability of alternative herbicide products in North America.

A downturn seems inevitable, says University of Arkansas weed scientist Ford Baldwin. "Other companies cant compete with glyphosate at $30/gal, and long-term we will lose herbicide choice."

That concern is echoed by Dale Shaner of Cyanamid. "Glyphosate tolerant crops have led to a 25% decline in spending on soya herbicides. Companies have already cut research spending as a result."

Weeds developing resistance to glyphosate is not considered a big risk, despite reports of ryegrass resistance in Australia. "But species shifts will happen very quickly for weeds with an extended germination period, especially if growers fall into the trap of continuous use of glyphosate," he warns.

Polygonums and solanums could fall into that category, increasing the need for alternative herbicides when fewer are available, he concludes. &#42

Clubroot research urges GM caution

Detailed research into the lifecycle of the clubroot organism has shown it takes DNA from the host plant and incorporates it into its own structure. That could have relevance to the arguments for caution over genetically engineered crops, says clubroot specialist Geoff Dixon of Strathclyde University.

It may also explain why it is proving so difficult to breed brassica varieties with enduring resistance to the disease.

"There is still a lot of basic research to be done on the clubroot organism. But there could well be spin-off information relevant to our understanding of the ways in which genetic material might move around in natural populations," he told FW.

Simply add water for a 65p pint. Andy Janes (left) and David Mugglestone cheer the success of their new Miracle home-brewing venture which is boosting demand for top-quality malting barley. Launched last October with a £10,000 HGCA Enterprise Award, the £29.90 kit produces 10pts of beer in about three weeks from a hops/yeast/barley powder mix. Interest from the UK and abroad suggests the initial estimated need for 2000t a year of barley will soon be proved correct, says Mr Janes.

CATCH-UP spraying looks to be the order of the day this season, so downtime is the last thing any operator wants.

A few minutes spent preparing the sprayer now could pay dividends later in the year.

First rinse the spray tank fully and spray the rinsings out through the booms and nozzles, advises Novartis application specialist Tom Robinson. Then remove, soak and rinse the filters and nozzle tips and if using air induction bubble jets clean the venturi with an air line.

Replace nozzle tips, fill the sprayer with clean water and run the pressure to 5 bar to test for leaks. Then set the sprayer at the target pressure and measure the timed output of each nozzle tip using a measuring jug.

Ensure the nozzles are within  5% of the target flow rate. "Nowadays new nozzles are within  1%, so if you find worn tips replace the whole set and get two extras for field replacement," advises Mr Robinson.

To check application rate and spray monitor accuracy mark out 100m and time a run between the markers with the sprayer half full. Calculate speed using the formula in the box.

Last, using the chosen engine revs, conduct a static boom output calibration. Check the one minute flow rate from at least one nozzle in each boom section using a measuring jug, average the results and calculate the application rate using the second formula below.

If adjustments are needed ensure the required spray quality can be maintained by referring to the manufacturers chart, concludes Mr Robinson. &#42


&#8226 Thoroughly rinse sprayer, nozzles and filters.

&#8226 Check flow rates of all nozzle tips.

&#8226 Check forward speed: 360 divided by time in seconds to cover 100m = speed in kmh.

&#8226 Check sprayer output: average nozzle output (litres/min) x 600 all divided by speed (kmh) x nozzle spacing (m) = litres/ha.

See more