Corn hits 8-year high on tight supplies, unfavorable dryness in Brazil

* Corn rises to highest since 2013 on global supply woes

* USDA says 46% of U.S. corn crop is planted

* Soybean, wheat markets slump

CHICAGO, May 3 (Reuters) - Chicago Board of Trade corn futures hit their highest price since March 2013 on Monday on strong demand for limited U.S. supplies and concerns over dry weather hurting output in Brazil.

Traders continue to focus on tightening global inventories as U.S. farmers plant corn and soy for the autumn harvest, rather than selling crops held in storage bins.

In Brazil, the 2020/2021 second corn crop is estimated at 72.7 million tonnes, compared with 77.65 million previously, according to broker StoneX.

"The corn market continues to look for a price that will uncover adequate producer selling and the farmer's attention right now is mostly on getting the 2021 crop planted," said Tomm Pfitzenmaier, analyst for Summit Commodity Brokerage in Iowa.

Most-active corn futures ended up 6-1/4 cents at $6.79-1/2 per bushel, after earlier setting an eight-year high of $6.98.

CBOT July wheat, meanwhile, tumbled 16-3/4 cents to$7.18 per bushel. July soybeans fell 10-1/2 cents to $15.24 per bushel, and November soybeans that represent the autumn harvest ended up 5 cents at $13.44-3/4 a bushel.

Traders bought new-crop November soybeans on expectations that U.S. farmers will shift some acres to corn that they had intended to plant with soy, brokers said.

As of Sunday, 46% of the nation's corn plantings were complete, the U.S. Department of Agriculture said in a weekly report, topping analysts' expectations for 44%. That was up from 17% a week earlier and ahead of the five-year average of 36%.

In Iowa, the top U.S. corn-producing state, farmers were able to plant almost half of the state's expected corn crop during the week ending May 2, for a total of 69% planted, according to the USDA.

Nationwide soybean planting was 24% complete, compared to analysts' estimates for 25%.

"If there are any production concerns this summer," Pfitzenmaier said, "the new-crop soybean contract has a lot of upside potential."

(Reporting by Tom Polansek in Chicago. Additional reporting by Michael Hogan in Hamburg, Naveen Thukral in Singapore and Colin Packham in Canberra; Editing by Marguerita Choy and Sam Holmes)