At this time of year John Greene is usually preparing to welcome dozens of Slovakian strawberry pickers for another harvest at his farm in County Wexford in south-east Ireland.

The work is arduous and repetitive and he relies on their experience and stamina to get the fruit picked, packed and sold.

Greene surveyed his fields this week with foreboding. “I look out my window and there’s no one to pick it. None of them are on site at the moment.”

His pickers remain in Slovakia, immobilised by a continent-wide lockdown. It is a similar story for hundreds of thousands of other seasonal agricultural workers who cannot travel just at a time when Europe needs them for harvests.

Fruit and vegetable crops in Spain, Italy, France, Germany, the UK and other countries risk rotting in the fields – putrefying testaments to the coronavirus pandemic.

“It won’t be pretty,” said Eamonn Kehoe, a soft fruit specialist with Ireland’s agri-food agency, Teagasc. “If they don’t have the staff it won’t be picked. It’s a nightmare, a perfect storm.”

John Greene, owner of Greens Berry Farm in County Wexford, Ireland. Photograph: John Greene

He was referring to Ireland’s growers, but farmers and agriculture officials across Europe have equally grim warnings about abandoned fields and lost crops unless they can conjure improvised armies of pickers.

Spain, which is the EU’s biggest exporter of fruit and vegetables, is already feeling the impact. “We’re very limited at the moment when it comes to having enough hands to pick and harvest,” said Pedro Barato, the president of Spain’s largest farming association, Asaja.

The pandemic, and the restrictions to combat it, were affecting every region in Spain, he said. “The need for workers is only going to increase as the season wears on. We need people to be working in the fields, while also taking all the necessary health precautions. If we don’t have anyone in the countryside to harvest the products, they’re just going to stay there and there could be shortages.”

In the Andalucían province of Huelva, for instance, only 7,000 of the 19,000 Moroccan workers who normally come had arrived before Morocco closed its border to passenger traffic.

In Italy the need is even greater. Some 90% of its agricultural workers are seasonal, the majority from Romania.

Massimiliano Giansanti, the president of Confagricoltura, the Italian agriculture association, said the sector needed 250,000 people to reap spring and summer harvests and to maintain vineyards.

“Coronavirus and blocks on transport mean that people who usually come from afar can’t come, and those who come from within Europe need to do 14 days of quarantine upon arriving, and the same when they return home, so for this reason many prefer not to come.”

In Germany, which relies on about 300,000 seasonal workers each year, there is mounting concern that white asparagus – so beloved it is nicknamed “white gold” – and other vegetables will languish in fields.

The German government has launched a website called The Land Helps to link farmers with volunteers willing to help out with bringing in everything from hops to potatoes. The appeal has been made in particular to millions of people whose workplaces have closed and students whose exams have been cancelled.

France has lost many of its usual workers from Spain and Poland, as well as French workers who are at home sick or caring for children, causing a shortage estimated at 200,000 people.

African producers face their own crises. Pandemic-related restrictions have crippled Kenya’s exports of green beans and peas to Europe, prompting producers to send half their workers home on mandatory leave. South Africa, another important exporter, is enduring one of the world’s strictest lockdowns.

If some harvests wither meals may look a bit less colourful for a while, but Europe is not going to go hungry. Food supply chains remain robust and supermarkets are keeping shelves stocked.

And there is still hope that the continent’s fruit and veg will end up on dinner plates. Governments are trying to create “green lanes” to allow fresh produce to circumvent restrictions on travel and commerce. The European commission has guidelines to try to extend that flexibility to seasonal agriculture workers.

Many farmers are buying time by delaying harvests. Strawberry producers, for instance, are ventilating tunnels and removing their fleeces to lower temperatures and slow ripening. For John Greene this will push back his harvest from early May to early June – enough time perhaps for the Slovakians to make it to Wexford.

Strawberries at Greens Berry farm in Wexford, Ireland. Photograph: John Greene

The great hope is that across Europe students, refugees, the newly unemployed and others - what France’s agriculture minister, Didier Guillaume, calls a “shadow army” of workers - will flock from cities to save harvests.

Meanwhile, the Country Land and Business Association has channelled the UK’s second world war blitz spirit by calling for a “land army” of new farm workers in England and Wales.

Italy’s agriculture minister, Teresa Bellanova, wants unemployed people to help farmers and work permits to be issued for asylum seekers and migrants. “For those who do not have legal documents, but who have perhaps worked in the fields, they should become legalised,” she said.

Many are sceptical city dwellers will respond: agricultural work can be tough, and another deterrent is fear of infection. But some people are already helping.

In the Seine-et-Marne department east of Paris around 70 people from five migrant and asylum seeker shelters responded to the prefecture’s call to harvest berries and asparagus. They will receive contracts and at least the minimum wage. However, some refugee advocates worried about “modern slavery” while rightwing activists complained about their presence in France.

Hundreds of people have volunteered to help bring in the asparagus harvest in Brandenburg, the state surrounding Berlin.

The crisis may have a silver lining. Consumers, perhaps to boost immune systems, have become healthier eaters, said Janusz Wojciechowski, the European commissioner for agriculture and rural development. “Consumption of fresh fruit and vegetables in the EU has been booming in recent weeks.”