President Gotabaya Rajapaksa banned chemical fertilisers this year to set off his organic race but tea plantation owners are predicting crops could fail as soon as October, with cinnamon, pepper and staples such as rice also facing trouble.

Master tea maker Herman Gunaratne, one of 46 experts picked by Rajapaksa to guide the organic revolution, fears the worst.

"The ban has drawn the tea industry into complete disarray," Gunaratne said at his plantation in Ahangama, in rolling hills 160 kilometres (100 miles) south of Colombo.

"The consequences for the country are unimaginable."

The 76-year-old, who grows one of the world's most expensive teas, fears that Sri Lanka's average annual crop of 300 million kilogrammes (660 million pounds) will be slashed by half unless the government changes course.

Sri Lanka is in the grip of a pandemic-induced economic crisis, with gross domestic product contracting more than three percent last year, and the government's hopes of a return to growth have been hit by a new coronavirus wave.