Wheat futures in Chicago fell on Friday, heading for their biggest weekly drop since September after weaker-than-expected U.S. export sales highlighted weak demand and competition from cheap Russian grain.

December Chicago (CBOT) wheat futures were down 0.4% at $5.51 a bushel by 0705 GMT and down 4.2% for the week.

CBOT soybeans fell 0.4% to $13.54 a bushel, but were still about 0.5% higher on a weekly basis. Corn fell 0.4% to $4.73 a bushel, up 1.9% from last Friday's close.

Prices have been near three-year lows since September as Russia posted a second straight huge harvest, continues to export huge quantities of cheap grain.

"There is still a lot of cheap Black Sea grain coming into the markets and keeping prices under wraps," Australian Crop Forecasters' Rod Baker said.

According to him, relatively low harvests in Argentina and Australia mean that the Asian importers will have to be diverted for deliveries in the coming months.

At the same time, the International Grains Council raised its forecast for global wheat production for 2023/24 by 2 million tonnes to 787 million tonnes.

However, Strategie Grains predicts less common wheat area in the European Union next year. Brokerage firm StoneX lowered its forecast for Brazil's 2023/24 wheat crop, while the Buenos Aires Grain Exchange cut its forecast for Argentina's wheat crop.

In terms of acreage, the Buenos Aires Grain Exchange said it expects more land to be planted with soybeans and less with corn for the new season due to late rains.

In maize, the International Grains Council raised its forecast for global production for 2023/24 by 4 million tonnes to 1.223 billion tonnes, raising its forecast for the US crop to 387 million tonnes.

Overseas corn prices are hovering near three-year lows amid ample supply