GRAINS-Chicago wheat futures firm on recent dollar slide, winter weather

By Renee Hickman

Jan 29 (Reuters) - Chicago wheat futures firmed on Thursday as a recent plunge in the dollar continued to support commodities priced in the U.S. currency and harsh winter weather threatened crops in the Black Sea region and the United States.

Corn traded near flat and soybeans ticked down slightly on expectations of a large South American harvest.

The dollar index =USD rebounded after tumbling to a four-year low on Tuesday, with U.S. President Donald Trump's reference to its value as "great" fuelling expectations of further weakness.

But the dollar's recent plunge was still weighing on investor positioning, traders said.

Arlan Suderman, chief commodities economist at StoneX, said the slide prompted a flow of money into hard assets.

A sharp rise in crude oil, driven by concerns about possible U.S. military strikes against Iran, also underpinned grains and oilseeds, which are partly used for biofuel. O/R

The most-active wheat contract Wv1 on the Chicago Board of Trade was up 3-1/2 cents at $5.39-1/2 a bushel by 12 p.m. CST (1800 GMT), after reaching its highest point since December 2.

CBOT corn Cv1 traded flat at $4.30 a bushel, while CBOT soybeans Sv1 fell 2-3/4 cents to $10.72-1/4 a bushel.

In top soybean producer Brazil, grain cooperative Coamo said it expects its 2026 harvest to be the largest ever.

The prospect of a bumper Brazilian soybean harvest was tempering concern about parched conditions affecting some soy and corn crops in Argentina.

In wheat, adverse weather conditions in growing regions of the Black Sea and the U.S. created some support, although it could be hard to sustain a rally based on adverse weather in January, Suderman said.

Agricultural consultancy Sovecon on Tuesday raised its 2025/26 Russian wheat export forecast, underscoring a hefty surplus in the world's biggest wheat-exporting nation.

The U.S. Department of Agriculture said net U.S. wheat export sales in the week ended January 22 totaled 558,201 metric tons for shipments in the 2025/26 marketing year. The sales were near the high end of a range of trade estimates.