Argentine farmers on Wednesday announced a return to their roadblocks just over a month after a crippling 21-day strike sparked by a rise in export tariffs, causing an immediate spike in international grain prices.

News of another strike in Argentina, the world’s third-biggest exporter of soyabeans and biggest of soya oil, immediately pushed soyabean futures up 2.5 per cent in Chicago to $12.96 a bushel.