Wheat jumped to its highest since early April on short-covering, while soybeans were little changed, weighed down by U.S.-China trade tensions.
The most-active corn contract on the Chicago Board of Trade has climbed 8.5% this week, the biggest weekly gain since July 2015. Corn hit a high of $3.82-1/4 a bushel on Friday the highest since Jan. 22.
Wheat is up nearly 11% this week, the biggest weekly climb since June 2017 and soybeans have added 4%, the first weekly gain in six weeks.
Rains across U.S. Midwest are threatening to further slow corn planting which could prompt farmers to switch to soybeans which are planted later.
"Corn prices rallied sharply and hold those gains," said Tobin Gorey, director of agricultural strategy at Commonwealth Bank of Australia.
"Moreover, the weak momentum that triggered at least some selling is close to being extinguished. Momentum investors will be getting buy signals."
Farmers had seeded 30% of the U.S. 2019 corn crop by Sunday, the U.S. Department of Agriculture (USDA) said on Monday, well behind a five-year average of 66%.
Crop consultancy Strategie Grains has again cut its forecast for this year's wheat and barley production in the European Union, partly due to drought in Hungary, but said recent rain across the EU had eased dryness and left decent harvest prospects.
In a monthly cereal report published on Thursday, the French firm reduced its projection for EU soft wheat production in the upcoming 2019/20 season to 143.9 million tonnes from 144.8 million forecast in April.
An escalating U.S.-China trade war continues to weigh on soybean prices.
U.S. President Donald Trump has dismissed the ongoing trade war with China as a "little squabble," but there are clear signs of the conflict already having an impact on the economy, and the stock market has become jittery again.
Commodity funds were net buyers of CBOT corn, wheat, soybean, soyoil and soymeal futures contracts on Thursday, traders said.
Trader estimates of net fund buying in corn ranged from 24,000 to 40,000 contracts. The following table reflects the average of estimates from trade sources