Russia says its wheat harvest will be down more than a third this year after a record drought.
Last year the world's third largest grain exporter harvested 97 million tons of wheat and exported 21.4 million tons. Its forecast this time is 60 million tons.
Prime Minister Vladimir Putin said the government will not lift its ban on wheat exports until the end of the year. The ban, announced last Thursday, has already pushed up world wheat prices.
"The question is what the country will be left with next year," Mr Putin said. "Most of the country's regions will enter the new year without winter crops."
Russian farmers already have little incentive to export as grain prices have been rising even faster in Russia than on world markets.
The drought is one of the worst in decades with much of the country suffering the hottest summer since record-keeping began 130 years ago.
But wildfires raging through western Russia have spread into farmland and there are fears that more fields will be lost.
Experts say the United States, Argentina and Australia will gain the most from the surge in wheat prices, because Canada and the European Union are not expected to have abundant harvests this year.