GRAINS-Chicago wheat edges lower but Black Sea export threat looms

The USDA lowered its condition rating for the U.S. corn crop for a third consecutive week following hot, dry weather in the Midwest. It said 61% of corn was in good-to-excellent condition, as of Sunday, down from 63% a week earlier.

The USDA kept its soybean condition rating unchanged at 63% good to excellent. The ratings for both soybeans and corn were the lowest for this point in the growing season in three years.

CANBERRA, Aug. 4 (Reuters) - Chicago wheat futures edged lower on Tuesday but held on to most of their gains from the previous session as fighting between Russia and Ukraine reduced exports from the Black Sea.

The most-traded wheat contract on the Chicago Board of Trade (CBOT) Wv1 was down 0.4% at $6.48-1/2 a bushel, as of 0649 GMT, after rising 1.8% on Monday.

Ukraine and Russia have been using drones and missiles to attack one another's ships and ports, disrupting shipments. Both nations are major suppliers of wheat.

Russian export prices fell last week under pressure from rising freight rates and insurance premiums, analysts said, though they still expect Russia to ship more wheat in August than in July.

There is scope for further price gains, said Andrew Whitelaw, an analyst at consultants Episode 3 in Canberra.

"In the next few months we will potentially see significant impact on exports," he said. "The market's not fully pricing it in."

CBOT wheat is up around 28% so far this year, mainly due to drought in the United States that shrank its winter wheat harvest and reduced global supply. Harvests elsewhere in the world have been mostly good, however.