21 February 1997

Herbicide additive can give extra perk to pgrs

GROWING evidence of the value of adding a carefully controlled amount of herbicide to traditional wheat growth regulators is emerging from France. Now the idea is being extended to the late season market for both wheat and barley.

Cyanamids Meteor contains a minute dose of soya and maize weed-killer imazaquin – as well as chlormequat and choline chloride (as in 5C Cycocel).

Average yield increases in the absence of lodging have been 4.7%, says UK technical director Angus Robinson. But the products proven role in stimulating root growth has been particularly valuable in 19 unlodged trials on light land in the past two dry years.

Mean yield boost was 6.7%. "When water is limiting, having more roots must be a good thing."

Detailed laboratory studies by Prof Armand Guckert at ENSAIA (part of the National Polytechnical Institute of Lorraine) in France confirm that Meteor increases root surface area. Other compounds are claimed to do likewise, he says. "But I have never found scientific literature to back that."

Imazaquin used as a herbicide in the US is applied at rates of about 100g/ha. Early French work confirmed that just 2g/ha eased the path of chlormequat into the plant. One spin-off is a widening of the optimum application window, which for chlormequat alone is quite tight. "With Meteor you have almost a 20-day window to get the chlormequat into the plant," says Mr Robinson.

Recent field trials reinforce the belief that a bigger rooting system lets crops make better use of nitrogen, says Prof Guckert.

Experiments showed it was possible to get the same yield from a Meteor-treated crop as an untreated one given 30kg/ha more nitrogen, because of better N uptake from the soil, he explains. "We also got a significant increase in the protein content of the grain."

Other benefits beyond the use of straight chlormequat include increases in flag leaf area and chlorophyll content, and a two-day delay in crop senescence – all of which potentially raise yield, explains Prof Guckert.

&#8226 Adding imazaquin to chlormequat and ethephon to provide a safer late-season regulator looks promising, according to ENSAIA . Meteor-like benefits have been seen in winter wheat, but have yet to be confirmed in barley.n


IMAZAQUINS ROLE


&#8226 Eases path of pgrs into crop.

&#8226 Broadens application window.

&#8226 Boosts root growth.

&#8226 Extends growing season.

&#8226 Offsets chlormequat "bounce-back".

&#8226 Promising in late season use.