11 April 1997

Salty mix sticks at late beet weed control

TAKE a pinch of salt and sugar extract, add water and stir. What have you got? According to one Lincs farmer, the best recipe to kill problem weeds in sugar beet.

David Tonge, who grows 4.8-6.5ha (12-16 acres) of the crop at Chapel and Anchor Farms, Martin Dales, near Woodhall Spa in Lincs, has been plagued by late germinating redshank and white willow weed on his black fen soils.

The soil has a large weed bank. "Left alone, redshank and white willow weed grow as big as young gooseberry bushes," says Mr Tonge.

Both weeds germinate late, so Mr Tonges two routine Betanal Tandem sprays applied soon after crop emergence have no effect. Even four subsequent passes with a tractor hoe fails to kill them all.

He decided a change of tactic was needed and decided to exploit the herbicidal activity of the fertiliser product Chilean nitrate of soda, a form of salt widely used in the 1930s as a herbicide.

"I first tried it 10 years ago. It worked reasonably well, but it did not seem to stick to the leaf, so control was not all that it could have been." He tried most adjuvants on the market. Some offered no improvement, others damaged beet plants.

After four years of struggle, he wrote to Mandops. "As it happened the firm had a product which it thought could be developed as a sticker for the salt spray."

Mr Tonge agreed to develop the sticker, which looks like thin molasses. After some fine-tuning he has been using it successfully for the past six years. "It works extremely well, provided you take a bit of care when you apply it." The salt concentration must be correct. Mr Tonge uses a hydrometer to measure the concentration of the spray solution, aiming for a reading of 1.208 when using nitrate of soda.

With vacuum-dried salt, Mr Tonges most common source, that equates to about 315kg/1000litres (2.8cwt/100 gals). "It helps if you have a black tank to store water in overnight. That warms it and helps to dissolve the salt faster," says Mr Tonge. He then adds enough of the formulated sticker product, called BeetnLow, at the label rate of 11 litres/1000 litres (9 pints/100 galls)

The mix is applied as a patch treatment – most of the weeds occur in the black peat holes. Application rate is 320 litres/ha (30 gals/acre) to ensure good coverage. Mr Tonge uses standard 200 litre/ha (18gal/acre) nozzles at about 2.5 bar, but travels at about 3mph to raise the volume applied.

One spray is usually enough to wipe out redshank and white willow weed. Cost is about £14/ha (£5.70/acre) for the salt, and £10.50 (£4.25/acre) for the BeetnLow. &#42

Salt + sticker = no weeds. David Tonges late weed problem in sugar beet has disappeared thanks to a novel mix which has improved control on his Fenland farm.