By Julie Ingwersen

Benchmark Chicago corn and soybean futures climbed to one-month highs on Monday, each rising nearly 4%, as worries about crop weather in the Midwest and Europe, and speculation about Chinese demand, spurred buying after a U.S. holiday weekend.

Wheat also gained ground, though a firmer dollar and prices in a Saudi tender viewed as aggressive underlined strong export competition.

As of 12:55 p.m. CDT (1755 GMT), Chicago Board of Trade December corn (CZ26) was up 16 cents, or 3.6%, at $4.57-1/2 per bushel, after reaching $4.58-3/4, its highest level since June 4. November soybeans (SX26) were up 44-3/4 cents, or 3.9%, at $11.92-1/2 a bushel after hitting $11.97.

CBOT September wheat (WU26) was up 14-3/4 cents at $6.14-1/2 a bushel.

Forecasts called for warmer-than-normal temperatures across the U.S. midsection next week, fueling weather worries as the nation's corn crop begins its critical pollination stage. Over the Independence Day weekend, heavy rains swamped fields in parts of Iowa, Illinois, Wisconsin and other areas, said Jack Scoville, vice president of the Price Futures Group in Chicago.

"There's a lot of questions as to whether we will get the corn production we were expecting this year, not only here, but in Europe," Scoville said.

Ahead of the U.S. Department of Agriculture's weekly crop progress report due later on Monday, analysts surveyed by Reuters on average expected the agency to raise its U.S. soybean ratings while leaving corn ratings unchanged.

Meanwhile, ratings for France's maize crop hit their lowest level in 13 years after last week's record heat wave, official data showed on Friday.

A smaller-than-expected quarterly reading of U.S. corn stocks released by the USDA last week magnified the importance of 2026 production prospects.

"After the USDA lowered their grain stocks last week ... a smaller yield to the U.S. corn starts to make the carry-out in the U.S. tight," Cory Bratland, hedging strategist with AgMarket.Net, said in a client note.

Traders continued to monitor Chinese buying of U.S. soybeans and potentially other crops, after May's summit between the countries' leaders produced a pledge to expand agricultural trade.

Speculation about Chinese interest in U.S. crops re-emerged before the holiday weekend and remained a supportive factor for prices, despite a lack of indications of deals, traders said.

Wheat futures followed the firm trend. Saudi Arabia booked 661,000 metric tons of optional-origin wheat in a tender, the country's state buyer said. Russian wheat could pick up a large share of the sales, traders said.