Norfolk farmers fear this year's harvest could grind to a halt unless key field operators are made exempt from self-isolation during the growing "pingdemic".
Many businesses are struggling with staff shortages as thousands of people are told to self-isolate after being "pinged" by the NHS Covid-19 app.
And although some workers in the food chain, such as processing plants and distribution centres, have been made exempt to keep shop shelves stocked, farmers have not been specifically included.
And that has sparked concerns for East Anglia's harvest as farms launch time-critical operations to gather their crops of wheat and barley.
The government says there is a process which will allow "named individuals in critical sectors" to leave self-isolation, under specific controls, in exceptional circumstances "where there would otherwise be a major detrimental impact on essential services".
But farming leaders said the measures must go further to ensure vital harvest teams can operate.
Gary Ford, East Anglia regional director for the National Farmers' Union (NFU) said: “Farmers are understandably concerned about the ongoing situation and how it might impact on harvest if they, or key farm workers, have to self-isolate under Covid-19 quarantine regulations.
"We’re in a crucial period for our vital agricultural sector in East Anglia. We are continuing to monitor the situation and to liaise with government at a senior level."
One farmer already affected is Tom Pearson, farm manager at the Raynham Estate near Fakenham, who has been told to self-isolate until next Monday after being in close contact with someone who had tested positive for Covid-19.
"We are starting harvest this week, but I cannot go out to manage on the farm," he said.
"It is frustrating, but it is not so bad for me as I am not a combine operator. The issue would be if one of my guys tests positive or gets pinged the farm would literally come to a standstill and the harvest won't happen.
"Why farmers are not classed as key workers under the food production classification is beyond me. We are the ones that produce the food for the hauliers to take to the supermarkets."
James Beamish is farm manager at the Holkham Estate in north Norfolk, which is at a crucial phase of its harvest with the winter barley is almost done, and the wheat expected to be ready in about 10 days.
"If a member of the team got pinged, we all work relatively closely together, so it could quite literally stop harvest operations," he said "Some of the derogations came in the food processing and delivery, but there is this old adage that food does not grow on the shelves.
"It seems strange - we were key workers last April, but now when it is time-critical getting crops of the field, we are not."
Mike Wilton, farm manager at the Stody Estate, said while none of his harvest staff have been pinged, he is "terrified of the prospect of it happening".
"We are being very cautious, and if anyone gives any hint they have got anything of that nature we will make them take a test," he said.
"We have had one member of office staff being pinged, but none of the farm staff. We have a team of six and, as a work community, they all live in each other's pockets so the chances are if we lose one we could lose them all. That would be a big problem.
"You cannot suddenly go to a job centre and say you need a combine driver."
A government spokesperson said: “In exceptional circumstances - where there would otherwise be a major detrimental impact on essential services - a limited number of named workers may be able to leave self-isolation under specific controls for the purpose of undertaking critical work only.
“This is a short-term measure before the exemption for fully vaccinated contacts is introduced on 16 August. It is highly limited and focused to prevent public harm from disruption to critical services."
Will this affect food prices for consumers?
Although the pingdemic has the potential to delay the harvest for individual farm businesses, this is unlikely to have a knock-on effect on food supplies or prices at the shops.
Wheat and barley are globally-traded commodities, so their supply, demand and prices are always fluctuating as a result of weather or political issues around the world.
These changes do not have an immediate effect on shop prices, as shortfalls in one area are covered by surpluses in another.
And the government has pointed out that fully-vaccinated workers will be exempt from self-isolation from August 16 - and most of the main wheat crop is expected to be harvested after that.
Andrew Fundell, an agri-business consultant and partner at Brown and Co in Norwich, said: "Fluctuations in commodity prices do not immediately affect prices on the supermarket shelves, so we should not be too alarmist about this.
"Delaying harvest by 10 days could be a concern individually, and there is a risk of the quality falling off. That is the worst circumstance. But it is unlikely we are going to see any wheat harvested before August 5 anyway.
"To allay the fears of consumers, the industry has been facing this [Covid] for 18 months and everything has still happened. One of the great things about Norfolk agriculture is that if one farming business is up against the wall, quite often you get people around to help out."
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