Expert trials alternatives to PDQ

Potato growers' favoured weed-control combination of Alpha Linuron and PDQ (diquat + paraquat) "is going to be a tough act to follow", following the EU-wide ban of paraquat.

This was the claim of AgroChemex agronomist John Keer, who carried out a series of trials supported by the Potato Council across the country to evaluate the efficacy of newer contact herbicides - such as Bayer's Basta and Syngenta's Retro - that have been brought onto the market to try to fill the gap left by paraquat's removal.

He also tested and compared several residual herbicide mixtures to see if they could cancel out the use of contact herbicides.

Paraquat has been widely used by growers as a pre-emergence contact weed-killer since the 1960s but was banned last year after a ruling by the European Court. Growers were given until last Friday (11 July) to use up their stocks of the product - which has a long half-life.

Keer said: "More than 70 per cent of the UK potato acreage was treated with a mixture of residual herbicide and paraquat (PDQ).

"There's really been no reason to look at (anything else) and so there's been a dearth of activity in the weed-control area. But we have lost PDQ and are likely to only be able to use a small amount of Linuron in the near future. At present the best estimate is that the maximum Linuron rate will become 1.31ha - Linuron and PDQ will no longer be an option."

Keer trialled various combinations, including:

Trial one (pre-emergence of crop)

  • - Alpha Linuron + Sencorex (1.3 litres + 0.5kg) - Keer said this is "what I think we can use next year";
  • - Alpha Linuron + Sencorex + Centium (1.3 litres +0.5kg + 0.15 litres) - Keer said he was "looking at it for next year";
  • - Defy (5 litres);
  • - Artist (2.5kg).

Trial two (50 per cent crop emergence)

  • - Basta (2 litres and 3 litres);
  • - Shark (0.33 litres);
  • - Alpha Linuron + PDQ (2.0 litres + 2.0 litres).

Keer concluded that, although Alpha Linuron + PDQ was the only combination that provided "100 per cent weed control", Alpha Linuron + Sencorex + Centium was "a treatment that works".

He said: "We looking at it for next year. I do not think that we have too much to fear from the loss of PDQ. The loss of Linuron, however, would be a much harder act to follow."

Kerr said that Basta and Retro, in combination with Activator 90 (2 litres + 0.2 litres), "did a good job" apart from on small nettles.


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