Herbicide trials highlight differences in beet weed control programmes

FINDINGS from the first year of a new three-year herbicide trials programme have highlighted differences between weed control approaches in sugar beet in terms of efficacy on key weed species, cost and crop safety.

The trials, which are a joint project between Broom’s Barn, British Sugar and Rothamsted Research, aim to provide growers with an independent comparison between herbicide systems.

The cost of herbicide programmes tested ranged from FAR at £75/ha (£31/acre) to manufacturers’ treatments at £120/ha (£50/acre).

The cost of spraying was also taken into account, based on the time it took to get a herbicide mix into the sprayer tank (3,000 litre tank, mix to cover 30ha (74 acres), applied in a water volume of 100 litres/ha).

With the FAR approach requiring application of several cheaper active ingredients compared to manufacturers’ approaches, which were based on fewer applications of more expensive products, consideration of application costs evened up overall programme costs, British Beet Research Organisation’s (BBRO) Dr Pat Turnbull told its winter conference at Peterborough.

Comparison

“The Bayer system scored well because of a relatively low inclusion rate, with just two products being mixed. With DuPont’s Broadacre we had six products in the mix, but in balance, we only applied Broadacre twice,” she said.

Trials results varied between sites and soil types, although in all cases weather delays meant weeds were generally larger and softer than normal when herbicides were applied and emergence continued late on into the season.

On a clay loam site at Broom’s Barn in Suffolk, where black bindweed and scarlet pimpernel were the main weeds present, all treatments controlled black bindweed well.

On a much lighter loamy sand at Broom’s Barn, delayed approaches performed well, primarily because they controlled late germinating fat hen.

However, a significant yield dip was observed at this site with the triflusulfuron-based Broadacre approach, which affected crop vigour.

However, the Broadacre approach performed well at the other sites and the effect could be avoided by not applying to ‘soft’ crops, said Dr Turnbull.

At Bracebridge Heath, Lincolnshire, on limestone brash, there was little difference between treatments in terms of control of ‘reasonable’ populations of the main weed species present - black bindweed and ivy leaved speedwell.

All of the herbicide programmes tested struggled on black fen at Holme Fen, near Peterborough, Cambridgeshire. With 97 weeds/sq.m in untreated plots and more than 20 different species present, the site was a challenging one, said Dr Turnbull.

Summary of BLW herbicide programmes tested

  1. Standard or conventional system – based on contact material, mainly phenmedipham, applied mainly at expanded cotyledon stage of weeds, pre-emergence of crop with 10-14 days between sprays
  2. FAR – phenmedipham, activator, residual. Low rates of active ingredients mixed together and applied to very small weeds at seven day intervals early on, possibly moving out to 10 days later
  3. Manufacturer programmes – formulated products containing several active ingredients, with a residual typically added. They are considered to be broad spectrum in activity, with applications starting at a slightly larger stage of weed size. Also considered to be more flexible, with a wider spray window.
  4. Broadacre approach (DuPont), relying on sulphonylurea Debut and high rates of contacts and residuals. The aim of this system is to use two big hits, 14 days apart on larger weeds

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