Chicago wheat slid for a sixth consecutive session on Wednesday, after sharp gains overnight as supply jitters caused by a Russian strike against a Ukrainian port were tempered by strong Russian exports and signs Moscow is open to reviving a Black Sea corridor deal.
Soybeans dipped to nearly one month lows and corn eased, as pressure from crop-friendly weather forecasts outweigh demand prospects.
The most-active wheat contract on the Chicago Board of Trade (CBOT) fell 15 cents at $6.37-1/4 a bushel by 10:15 a.m. (1615 GMT), its lowest since July 13 after earlier rising nearly 5%.
CBOT Soybeans lost 21 at $13.20-1/4 a bushel, after reaching its lowest since July 7.
CBOT corn eased 9 cents to $4.98-1/4 a bushel, falling for a seventh consecutive session.
The Russian attack on southern Ukraine early on Wednesday, which struck grain facilities at Izmail on the Danube, underscored the risk of a further squeeze on Ukrainian exports after Moscow last month quit an agreement allowing grain shipments from Ukrainian Black Sea ports.
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However, wheat futures shed most of their initial gains as the market weighed the attack's impact on global supplies.
"If Russian wheat exports were disrupted, that's a game changer. But the game, as far as Ukraine goes, has already been changed," Joe Vaclavik, president of Standard Grain, said.
Russian President Vladimir Putin told Turkish counterpart Tayyip Erdogan on Wednesday that Moscow was ready to return to the Black Sea grain deal as soon as the West met its obligations regarding Russia's own grain exports.
Cooler, wetter weather forecast across the U.S. Midwest in August continue to pressure corn and soybean prices.
"The USDA yield at 52 bushels per acre is looking more likely to happen. We haven't had enough weather stress on soybeans to cut that yield substantially," Karl Setzer, commodity risk analyst at Agrivisor, said.