Many Ukrainian farmers have gone to the front lines to fight, and the farms they left are being ravaged by Russian shelling. That means Ukraine’s spring harvest of barley, corn, and other crops — projected to be a strong season before the war — will be less than half of the 2021 level, the Agriculture Ministry says. Ukraine banned exports of wheat and other food last month to secure its own wartime supplies, but at this point it can’t really export anyway: Russian warships are blocking access to its Black Sea ports and have bombed at least three civilian ships carrying Ukrainian goods. Ukrainian farmers will likely also miss their coming planting season, and those who are still in the fields have scrapped export crops in favor of foods that can be quickly harvested to feed civilians and soldiers. Russia’s own ability to export, meanwhile, has been hamstrung by sanctions.

While the two countries generate about 30 percent of the world’s exported wheat, that’s still less than 1 percent of the world’s total wheat — and other producers, such as India, grew more wheat last fall in anticipation of a Black Sea conflict. But it takes time for recipient countries to rearrange their supply chains and place orders with new sources. And the supply of labor to deliver those orders is running short, as Russians and Ukrainians together make up about 15 percent of the world’s shipping workforce. Panicked investors have sent wheat prices soaring by as much as 50 percent, and civilians have resorted to hoarding, particularly in Arab countries that depend on imports for staple foods. Those countries are already rationing. Egypt, which relies on Ukraine and Russia for about 85 percent of its wheat imports, has now fixed the price of bread, while Tunisia is limiting sales of semolina, used in couscous.