"If we have less free movement of labour a new (seasonal labour) scheme would be a priority," he said. "It's likely that Brexit will lead to greater restrictions on labour but even without that we would still need another scheme. Last year a poll of 300 growers found one-third struggled to meet their labour needs."
He added: "Our main concern was labour even pre-Brexit as costs are rising under the National Living Wage, which has the capacity to put firms out of business in the next four or five years. Even the best and most efficient growers are saying 'we can't see this remaining viable'. We can't simply wait for automation to arrive. Instead we will just export production to where labour is available and affordable. We are already seeing an increase in UK growers investing abroad."
Meanwhile, seasonal labour is already declining in productivity, he suggested. "Initially you got the first flush of people who were very keen, but then that tails off. That's currently evident in other sectors of horticulture."
The options are a points-based system, which is already on the statute books, but whose third tier for low-skilled workers has been "mothballed" since its introduction in 2008; a visa system that for farming would "draw on SAWS" (the defunct Seasonal Agricultural Workers Scheme); and also the granting of the right to remain for EU citizens currently in full-time positions on farms.
The number of this last group has been put at 10,000 by the British Growers Association, said Hartfield. "Those already here need certainty. Then a top-up scheme could allow (newcomers) to work for up to five years. It's hugely challenging, but horticulture is not alone. There are some 5.5 million non-UK workers here. Without them, even if everyone in the UK currently unemployed was taken on, we would still be four million short."
Hartfield urged delegates: "Help us with lobbying. We need to hear from employers. Is there a tail-off in labour supply since Brexit?"
Meanwhile, on crop protection, he said: "We will need access to a greater range of products to remain competitive in global markets. The UK Government has long been critical of the EU's overcautious approach. We could harness the USA's IR4 system for approvals or harmonise with other non-EU countries."
On trade, he pointed out: "We have a £4.7bn trade deficit and rebalancing that is a huge opportunity for UK growers." Should the UK's trade relations with remaining EU countries default to World Trade Organization-mandated tariff levels, "this would make home produce more competitive but inputs more expensive". He added: "There is an opportunity to strengthen existing controls on plant health. But we need the right expertise put in place and resourced."
The NFU has set up a "Brexit unit" under former Crop Protection Association chief executive Nick von Westenholz. It is also "in the process of digesting" the results of its widest-ever membership consultation on the future of farming policy post-Brexit, he added.