Bears have overtaken bulls among wheat market speculators, as the lower price of crude oil and the stronger dollar weigh on commodity prices.

Non-commercial traders cut their long positions in Chicago Board of Trade wheat by 4,800 contracts in the week to September 9, figures from the Commodity Futures Trading Commission showed. The decline, coupled with an increase of nearly 2,000 in short positions on CBOT wheat futures and options took the total number of shorts to 66,300, outnumbering long positions by more than 3.600 contracts.

The switch, which was reflected in other commodities, was blamed on a double whammy of a weaker oil market, which has a knock-on effect on biofuels, and a strong dollar, which has historically been strongly correlated with weaker commodity prices.

Going long in commodities and shorting the dollar has been a popular and profitable trade in recent months.

"An investor who invested $100,000 in crude oil around August 2007 and at the same time bought euro for $100,000 was able to post a profit of $120,000 one year later," Commerzbank said in a research note on September 10.

"The recent appreciation of the US dollar and the decline in the oil price has seen the whole thing reverse."

Speculators also turned more bearish in Chicago corn, with long contracts down by 7,450 in the week and shorts up by 820. In soy, long positions were down by more than 10,000 and shorts up by 7,950.

In New York's ICE exchange, bears overtook bulls in cotton after closing 3,400 long contracts and raising shorts by nearly 5,000. Similar switches were seen in cocoa, coffee and sugar.