US President Donald Trump's threatened 30% tariff on South African exports is set to deal an economic blow to a community he has vocally and controversially championed: white farmers.

Citing false claims that white South Africans are being persecuted, Trump has cut aid to the country, publicly berated its president in the Oval Office and invited Afrikaners - descendants of early European settlers - to come to the United States as refugees.

But for white farmers who remain rooted in their homeland and aspire to keep making a living from the land, the tariffs due to come into effect on August 1 are an assault on those ambitions.

"It doesn't make sense to us to welcome South African farmers in America and then the rest that stays behind ... to punish them," said Krisjan Mouton, a sixth-generation farmer in Western Cape province's citrus heartland.

"It's going to have a huge impact," he said, standing among rows of trees heavy with navel oranges on his farm near the town of Citrusdal. "It's not profitable to export anymore to the USA."

After a three-month pause, Trump escalated the global trade offensive he launched in April, announcing tariffs on more than a dozen countries on Monday, including South Africa. 

Its citrus fruit, along with wine, soybeans, sugar cane and beef, had previously benefited from duty-free access to the US under the Africa Growth and Opportunities Act. 

Helped by that trade initiative, South Africa, the world's second-largest citrus exporter after Spain, generates $100-million annually from the US market. 

The new tariff ends that preferential treatment. And with three-quarters of South Africa's freehold land white-owned, white farmers will face the immediate economic fallout though they will not be the only casualties. 

Boitshoko Ntshabele, chief executive of the Citrus Growers' Association of Southern Africa (CGA) said the levy will hurt all South African farmers and farm workers, no matter their race.

"A 30% tariff would wreak havoc on communities that have, for decades, focused on producing specifically for the US market," he said.

'FARMERS WILL GO BANKRUPT'

Its location in the Southern Hemisphere means South Africa produces citrus at times of the year when the US doesn't, with its exports giving US consumers year-round access to fruit.

While the United States accounts for only around 6% of South Africa's citrus exports, some farming areas produce specifically for the US market.

Redirecting produce grown for the US to other markets is not simple, as size and plant health requirements vary from country to country.

Nestled in a valley in Western Cape's rugged Cederberg mountains, Mouton's family farm employs 21 permanent workers, and nearly triple that number during peak picking season.

The CGA has said about 35 000 jobs are at risk in Citrusdal alone, as the tariffs risk making South African citrus uncompetitive compared to fruit from Peru, Chile, and Australia.

South African President Cyril Ramaphosa has said trade talks with Washington will continue and argued that the 30% rate was based on an inaccurate understanding of the two countries' trade.

In the meantime though, the CGA wants to speed up an expansion of exports to new markets including China and India. High tariffs in some countries and stringent plant health requirements in the European Union, for example, make that a complicated prospect, however.

Not far from Mouton's farm, workers are carrying on as usual, for now, sorting and packing fruit at the 14 000-square-metre Goede Hoop Citrus warehouse. But if the 30% levy remains in place, that won't last long, managing director Andre Nel told Reuters.

"Farmers will go bankrupt. For sure there would be job losses within our sector," he said. "I don't even want to think about it."