Defy herbicide may mean easier potato weed control

Weed control in potatoes could become simpler this season with the UK launch of a product growers elsewhere in Europe have been using for over 10 years.

Syngenta’s Defy (prosulfocarb) came to the UK market last autumn with approval as a novel grassweed herbicide in cereals.

Now it is available for use pre-emergence on potatoes offering new levels of crop safety and control of a wide range of important weeds, including cleavers, black-nightshade and fumitory, says the firm’s Jason Tatnell.

Split-field trials on 50 UK farms last year comparing it against other products confirmed the commercial experience of growers in Germany, France, Holland and Belgium, he says. “One of the key benefits of Defy is its simplicity at a busy time of year.”

It may be used on all varieties, soil types and all supermarket and end-user protocols. And unlike other thiocarbamate residual herbicides it does not need incorporating, says Mr Tatnell. He describes the product as very ease to use, with straightforward recommendations and excellent crop safety margin even after heavy rain.

Tuber quality

Tests at Campden and Chorleywood Food Research Association have shown no detrimental effects on tuber quality whatever the target outlet – even at double the full 5 litres/ha recommended dose.

All other main residual herbicides for potatoes have some limitations, for example in terms of varietal restrictions and soil type, he notes. “Defy comes into a market where there are nearly always some headaches.”

The product may be applied up to crop emergence, 4 litres/ha providing control of the main weeds, 5 litres/ha offering more persistent cleavers control where crops sown at lower seed rates may take longer to reach full canopy.

Where weeds have already emerged PDQ (diquat + paraquat) at 2-3 litres/ha should be added, Mr Tatnell advises.

Defy may also be tank-mixed with 1 litre/ha of linuron to boost control of polygonums, fat hen, mayweed and poppy, or with metribuzin to help tackle polygonums on silts, heavy or high organic matter soils.


John Keer of independent consultancy Agrochemex welcomes Defy as a potential linuron replacement in mixtures.

Although linuron’s immediate future seems more assured than it did at one stage, the withdrawal of Temik [aldicarb] shows that nothing is certain, he adds. “The picture could change tommorow because of supermarket pressure”, says Dr Keer.

One of the favourite mixtures is 2-3 litres/ha of linuron with 0.25-0.75 litres/ha of Sencorex [metribuzin], the rates varying according to soil type. “A pre-em mix of 4 litres/ha of Devy and 0.5 of Sencorex has very few crop limitations. Two plus two of PDQ plus linuron is reliable, but its safety at the late stage is not the best. The safety of two of PDQ plus four of Defy is much better.”

At £6/litre, the standard Defy dose means control costs slightly more than other peri-emergence options, he says. “Defy’s a little bit more expensive than linuron, but not as expensive as the other cleaver-active residuals like Centium and Artist.”

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