Corn rose the most in a week in Chicago and wheat gained on concern wet weather will delay planting in the U.S. Midwest as dry weather in the southern Plains and Europe hurts winter-wheat prospects.

About 40 percent of the U.S. corn crop, the world's biggest, was planted as of May 8, below last year's 80 percent and the five-year average of 59 percent, the U.S. Department of Agriculture said in a report last week. Soil in the north of France, the biggest European Union wheat producer, was the driest in the past 50 years, Environment Ministry data show.

Wet weather along the Mississippi River that's flooding fields and drought in parts of Kansas, Oklahoma and Texas are curbing yield prospects in the U.S., the biggest exporter of corn, wheat and soybeans, and boosting commodity prices. Food costs soared to a record in February as prices of raw materials gained.

"Conditions for grains are looking less than ideal, with no major change expected," said Justine White, an analyst at researcher VM Group in London. "While corn planting areas continue to look soggy, major wheat-growing regions are struggling with drought, which will stress the crop. Dry conditions in the EU are putting pressure on wheat crops, which is a concern, as export demand is expected to be high."

Corn for July delivery added 11 cents, or 1.6 percent, to $6.93 a bushel by 1:15 p.m. London time on the Chicago Board of Trade, advancing for a third day. Prices rose as much as 2.6 percent, the most since May 9. The grain fell 0.6 percent last week, touching the lowest price in almost two months on May 12.

Eoin Treacy's view Inclement weather has contributed to high prices for agricultural commodities over the last year. Droughts in Europe and Russia, floods in Pakistan, Australia and elsewhere, warm nights in the USA last summer and the current floods have all contributed to solid fundamental reasons for the increase in prices. Historically low global inventories for many grains mean that the world depends on bumper crops to meet growing demand. At some point supply will return to medium-term dominance but that is looking less likely for this year.

Corn retested the 2008 peak a month ago and entered a period of mean reversion. It has held the progression of higher reaction lows and appears to be in the process of finding support in the region of 700¢. A sustained move below 600¢ would be required to begin to question the consistency of the medium-term advance.

Soybeans rallied impressively from July last year but began to lose momentum from February and entered a ranging consolidation which allowed a relatively gradual reversion towards the 200-day MA. Prices still exhibit a mild downward bias and the short-term progression of lower rally highs, currently near 1400¢ will need to be broken to indicate a return to medium-term demand dominance.

It has been almost a year since wheat broke out of its 18-month base; almost doubling in three months. It has been consolidating mostly above 650¢ since and is currently testing a potential area of support near the 200-day MA. However, a clear upward dynamic would be required to indicate the return of demand in this area. Oats has a relatively similar pattern.