3 August 2001

Pre-em weapon to control blackgrass gains approval

By Andrew Swallow

GROWERS have a new, more effective, pre-emergence weap-on to control blackgrass and other grassweeds in cereals this autumn, says BASF.

Crystal, its long-awaited flufenacet plus pendimethalin formulation, formerly known as ACH210, has now been approved. Growers will see a substantial improvement over current pre-emergence blackgrass standard tri-allate (Avadex), it claims.

Across 32 trials, including enhanced metabolism and target site resistant blackgrass, control was raised from 30% with 22.5kg/ha of tri-allate to 80% with 4 litres/ha of Crystal.

On 13 trials with triple R enhanced metabolism resistance – as bad as it gets – control was reduced to about 68%. But that was still well ahead of Avadex at 29%.

"There is a big step up in the level of action compared to Avadex," says technical manager Rob Gladwin.

A reduced rate of 3 litres/ha still had an edge on Avadex, giving averages of 54% and 39% control in the two trial series, respectively.

The flufenacet component of the formulation brings a new, but as yet unidentified, mode of action on blackgrass. Uptake is 80% through the roots and it is more soluble, hence more mobile, than pendimethalin.

"It needs to be used early in the season while the roots are near the surface. Later use places a greater reliance on the pendimethalin," says Mr Gladwin.

Pre-emergence or very early post-emergence, so-called peri-emergence, are the best timings, he says. As a spray-on product fewer growers will need contractors to apply it, another advantage over Avadex.

"Peri-emergence is when there is a green haze across the field, you can just pick out the tramlines. But my concern with the peri-emergence timing is that the weather could mean the timing is missed, control drops away quite rapidly post-emergence."

Besides blackgrass the label lists loose silky bent and annual and rough stalked meadow grass as susceptible, the meadow grasses at a 2 litres/ha rate.

Not on the label, but supported by BASF, are Italian and perennial ryegrasses, "susceptible", and wild oats and barren brome, "suppressed".

Pendimethalins inclusion at 300g/litre adds to grassweed control, extending residual activity into the spring and introducing control of a wide range of broad-leaved weeds.

But as with straight pendimethalin used pre-emergence, crop damage can occur when seed-beds become waterlogged shortly after application.

BASF says Crystal should always be used as part of a programme where blackgrass is the main target (see table).

Packed as a 10-litre emulsifiable concentrate, the product has a LERAP B rating and will be widely available this autumn. Price seems set to be at a premium to Avadex, though it is not clear whether BASF has included the contract application cost of Avadex in its calculations. That is typically £6-£7/ha plus £21-£22/ha for the product, says herbicide manager Andrew Jones.

"The price will reflect the benefits over current standards, and by that I mean tri-allate," he adds. &#42

Earliest blackgrass chit

Shoots of blackgrass already emerging where seed has shed this season should be seen as good news by growers, says ADAS arable technical manager James Clarke. "I think it is the earliest I have ever seen it chitting.

"It implies that the level of dormancy in the seed is low, so we should have the opportunity to get the weeds away early and get rid of them before the drill."

That will be crucial to off-set the high seed return resulting from widespread poor control last autumn, adds Mr Clarke.