Mrs Obama started work on the kitchen garden with a gang of schoolchildren last month. Media coverage of the first White House food plot since Eleanor Roosevelt “dug for victory” in the Second World War garnered media coverage across the world.

But to the consernation of Big Ag, Mrs Obama has said the project will not use chemical products to tackle pests or give her plants a boost, the Times reports.

Shortly after the digging began, Mrs Obama received a letter from the Mid-America CropLife Association (MACA), which represents the companies producing the pesticides and fertilisers underpinning “conventional” American agriculture, the paper said.

Addressed to “Mrs Barack Obama”, the letter congratulated the First Lady on “recognising the importance of agriculture in America”. Farming is America’s largest industry, generating 20 per cent of GDP and directly or indirectly employing 22 million people.

The letter avoiding the term “organic”, highlights the role of technological advances – technologies that can see a single acre produce almost 20 tonnes of strawberries of 110,000 heads of lettuce in a season – in modern agriculture.

“Today, an average farmer produces enough food to feed 144 Americans who are living longer lives than many of their ancestors. Technology in agriculture has allowed for the development of much of what we know and use in our lives today,” MACA wrote.

“If Americans were still required to farm to support their family’s basic food and fibre needs, would the US have been leaders in the advancement of science, communication, education, medicine, transportation and the arts?

“We live in a very different world than that of our grandparents. Americans are juggling jobs with the needs of children and ageing parents. The time needed to tend a garden is not there for the majority of our citizens, certainly not a garden of sufficient productivity to supply much of a family’s year-round food needs.”

The carefully-worded letter also “respectfully” encourages Mrs Obama to recognise the role played by conventional agriculture in feeding America’s growing population.