A combination of strong exports and weak production and depressed wheat stocks in Canada, the world's second largest exporter, to their lowest levels for 20 years, official statistics have shown.

Wheat stockpiles were, at 4.8m metric tonnes, 29.4% lower at the end of July than a year before, Statistics Canada said. "Total stocks have declined to amounts not seen since the late 1980s," the agency added.

The drop was particularly steep in durum wheat, the variety used in making pasta, where inventories fell by 31.8% to 842m tonnes. Farm stocks of durum slumped to 50,000 tonnes, compared with 300,000 tonnes a year.

Statistics Canada said that the fall in stockpiles reflected the smaller area of spring wheat planted in 2007, as well as "steady" export demand for durum. Canada is the world's second largest wheat exporter.

However, the data failed to revive wheat prices, with some traders saying they had expected an even bigger drop in stocks. On the Minneapolis Grain Exchange, where high protein spring varieties trade, hard red spring wheat closed down $0.10 at $7.80 a bushel.

Canada's canola stocks have also fallen, Statistics Canada added. At 1.5m tonnes, inventories of the oilseed were 15.3% lower at the end of July than a year before.

Barley stocks were, at nearly 1.6m tonnes, up 5.4% year on year, and oats, at 975,000 tonnes, 75% higher.