PARIS — When Europe tightened its borders to prevent the spread of the coronavirus, France’s biggest farmers sounded an alarm: The workers they rely on from other countries to harvest much of the nation’s food could no longer make the trip.

The concern is widespread. In Britain, farmers are struggling to find people to pick raspberries and potatoes. Part of Germany’s prized white asparagus crop risks rotting in the ground. And in Italy, over a quarter of the strawberries, beans and lettuce ripening in coming months may lack harvesters.

European governments have declared food supplies a matter of national security as millions flock to supermarkets to brace for prolonged home confinement. But border lockdowns have immobilized legions of seasonal workers from Eastern Europe who toil in fields from Spain to Sweden, forcing a rapid rethink of how to supply labor to those farms.

France’s agriculture minister this week trumpeted what sounded like a surreal call for hairdressers, waiters, florists and others temporarily unable to work at their mothballed businesses to head to the nation’s fields and start picking.