This is a lovely map published in 1952, by the United States Office of Foreign Agricultural Relations. At the most basic level, it is a snapshot of a slow-moving global crop epidemic. The coffee leaf rust (caused by the fungus Hemileia vastatrix) had first appeared in epidemic form in Ceylon in 1869. From there, it had spread through the Indian Ocean Basin and the Pacific. In the face of the Coffee Leaf Rust, coffee planters in Ceylon abandoned coffee cultivation in favour of tea, for which the island is now famous. The disease also devastated the coffee farms of Java, then another of the world’s major exporters of arabica coffee. Planters there switched to other crops, or (in some places) began cultivating robusta coffee (C. canephora, var. Robusta), a rust-resistant coffee that had recently been discovered in the Belgian Congo. Robusta helped in the recovery of many rust-wracked coffee zones, especially in the humid lowlands of the Indian Ocean Basin and Africa. But this rust-resistance came at the expense of quality; robustas did not have the same cupping quality as arabica. Robustas were usually used as cheap fillers in blended coffees. So this map shows not only the distribution of the rust, but also (approximately) the global distribution of arabica and robusta coffee in the mid-twentieth century. A few enclaves of arabica production in the Eastern Hemisphere did survive — especially in Kenya, Ethiopia, India, and Sumatra. But virtually everywhere else in the East, robusta prevailed.
In the early twentieth century, the rust gradually began to move across Africa, from east to west. And it became apparent that the vast fields of arabica coffee in the Americas were at risk from the coffee rust. It is also a warning to the coffee growers of the americas. The rust finally did appear in Brazil in 1970; by 1985 it had reached almost every coffee-growing region in the Americas. While it was seldom as catastrophic in the Americas as it had been in Ceylon or Java, it has been a chronic problem for coffee farmers in the Americas ever since.