Traders fear that the lateness of America's corn and soybean harvests will prompt "unusually small" plantings of winter wheat.

US farmers had harvested only 23% of the soybean crop by Sunday, well under a half the proportion normally in the silo at this time of year, Washington data has revealed.

For corn, only 13% of acreages had been harvested, down on the 35% typically in the silo by now.

The delays, reflecting poor weather as well as late plantings, have fuelled concerns that acreages of winter wheat will slump from the 43,300 acres sown for this year's harvest.

'Increasingly nervous markets'

"For the US, the largest wheat exporter in the world, this would imply a decline in supply. Against the backdrop of these crop delays, markets are becoming increasingly nervous."

Winter wheat has historically represented a far bigger proportion of US wheat production than spring-sown, accounting for 69% of this year's harvest.

'Promote nerves'

At Rabobank, analyst Nick Hungate told Agrimoney.com he had heard the rumours, which were helping to "promote nerves" among investors with short positions, which were particularly prevalent in wheat.

However, he also pointed to the apparent "dripping in" of fund money, many in long positions, and the weakness of the dollar, as a reason behind wheat's revival.

Nonetheless, wheat lost early gains to stand marginally lower in Chicago and Kansas in lunchtime trade on Friday.

Prices had already closed lower in London and Paris.