16 March 2001

Three-pass approach better bet for some

By Andrew Swallow

REPEAT low dose sugar beet herbicide applications under the FAR system may work well for some.

But two East Anglian growers have been there, done that and found a three-pass conventional programme more cost-effective.

The reason is a combination of weed spectrum and soil type, says agronomist Darryl Shailes of Hutchinsons. "FAR works well on light, non-shifting soils with an easy weed spectrum and plenty of moisture.

"But where there are more difficult weeds it can prove expensive because you end up going five or six times, and still not getting good control."

That was the case at Robert Leechs farm at Hockham, near Thetford in Norfolk. A standard FAR mix of phenmedipham, ethofumasate and metamitron or lenacil never totally got to grips with the weed spectrum on his sandy Breckland soil.

"We were always chasing the Charlock," says Mr Leech. "One year we spent £120/ha and still did not get on top of it."

Blowing soil and dry conditions meant little residual activity was gained from the metamitron, says Mr Shailes, and despite multiple doses, the phenmedipham (as in Betanal) struggled to kill the charlock with contact activity. "We were using up to 3.5 litres/ha of Betanal."

Now, a pre-emergence chloridazon/metamitron mix followed by a couple of carefully timed post-emergence applications is doing a better job, for less money and fewer passes (see table).

The difference is Debut (triflusulfuron-methyl) which, used as a post-emergence spray at 15g/ha plus 0.2 litres/ha of Venzar (lenacil) and oil, knocks out even quite large Charlock. Oilseed rape is also now grown in the same rotation as the sugar beet.

"We used to be terrified of volunteers and keep the rotations separate. Now it is not a problem," says Mr Leech.

Further south, just into Suffolk, Nigel Webber also went down the FAR route in the mid-1990s, but has since switched back. He grows 255ha (630 acres) of cereals, oilseed rape, peas and sugar beet at Home Farm, Barningham, and is a one-man band doing all his own spraying and spreading.

"The main benefit of the new system is that it gives me more time."

Mayweeds and cleavers are the key weeds on his sandy clay loam soils, plus a low level of oilseed rape volunteers. When the FAR system was used, it was preceded by a pre-emergence Spectron (chloridazon + ethofumesate) to sensitise the cleavers. The repeat low dose post-emergence programme started at first sight of the weeds.

"We used to go twice with a Betanal, Norton and Pyramin mix, five or six days apart as soon as the first cleavers emerged," says Mr Shailes. "Then wed have a look and often end up going again. If the cleavers got beyond a whorl it wouldnt control them and on this heavier soil it can be very difficult to travel every seven days."

Added to the hit-and-miss cleavers control, the sugar beet took quite a beating from such a system, he adds.

With Debut in the post-emergence mix cleavers can be left later, upto the second whorl, ensuring more weeds are taken out with each pass. Last year 0.5kg/ha of Goltix (metamitron) plus 2 litres/ha of Weedmaster (chloridazon) was applied pre-emergence, followed five weeks later by a desmedipham, phenmedipham, lenacil and trisulfuron-methyl mix.

"With cleavers the Debut rate needs to be at or close to full label rates. But we can do just two post-emergence sprays and generally be done," says Mr Shailes.

At £109/ha (£44/acre) the programme is not cheap, he concedes. "But I dont mind the cost so long as it does a cracking job," adds Mr Webber.

With Charlock the main target, Mr Leech reckons hes now saving £40/ha (£15/acre) compared to a five spray FAR regime.

"And we cost each pass at £7.50/ha, so that is £15/ha saved on a couple of extra passes – nearly the cost of another spray application." &#42

THREE-PASSPOLICY

&#8226 Pre-em treatment buys time.

&#8226 Debut allows post-em delays.

&#8226 Difficult weeds targeted.

&#8226 Cash and time saving compared to FAR for some.

Programmes compared

Charlock key weed

Pre-em 2 litres/ha choridazon.

1st post-em 1 litre/ha Betanal Compact + 0.2 litres/ha Venzar + 15g/ha Debut.

2nd post-em 1 litre/ha Betanal Compact + 0.4 litres/ha Venzar + 25g/ha Debut.

Total cost £79/ha (£32/acre).

Cleavers key weed

Pre-em 0.5kg/ha metamitron + 2 litres/ha chloridazon.

1st post-em 1.25 litres/ha Betanal Compact + 0.4 litres/ha Venzar + 25g/ha Debut + 0.5 litres/ha veg oil.

2nd post-em 1.5 litres/ha Betanal Compact + 0.2 litres/ha Venzar + 30g/ha Debut + 0.5 litres/ha veg oil.

Total herbicide cost £109/ha (£44/acre).

Betanal Compact = desmedipham + phenmedipham. Venzar = lenacil.Debut = triflusulfuron-methyl.