31 May 2002

Weather puts FAR beet weed control to toughest test yet

SUGAR beet growers following FAR weed control systems may need to beef up later herbicide mixes this season, says Morley Research Centre.

Two years of results from BBRO-funded work by the Norfolk-based research station show the phenmedipham plus activator plus residual system can give the highest margin over herbicide costs.

However, this seasons long, dry, cold spell followed by recent rains could see it come under its sternest test yet, says Morleys Martin Lainsbury.

Flushes of weeds are now emerging, but occasional large, frost hardened weeds among them will need a much more robust mix, he warns.

For large knotgrass Mr Lainsbury suggests a good rate of Goltix (metamitron) plus Betanal Expert (phenmedipham, desmedipham + ethofumesate) and oil. "Say 1.25 litres/ha of Goltix and 1.5 litres/ha of Expert provided every plant in the crop has at least two true leaves.

"Thats also a good mix for fat hen, but for bindweed leave out the Goltix and use Venzar (lenacil) instead," he adds.

Adding or increasing the desmedipham rate (as in Betanal Compact or Carrera) would also up the contact activity of the mix, a technique that has proved most cost effective in the BBRO FAR work on light soils, he notes.

"It is a very good choice in dry conditions."

On heavy soils where cleavers and brassica weeds are more likely to be a problem including 10g/ha of Debut (trisulfuron-methyl) from the second spray has given the maximum margin provided the residual is switched from Goltix to Venzar (lenacil) to avoid any possible antagonism between the metamitron and Debut.

However, where these weeds have got away Mr Lainsbury says the full 30g/ha Debut rate should be used, with 2.5 litres/ha of Betanal Flow and 0.4 litres/ha of Venzar Flowable. &#42

BEETWEEDTIPS

&#8226 FAR for best margins.

&#8226 Tune to soil type.

&#8226 Tough test this year.

&#8226 Raise rates for escapees.