Coffee leaf rust — Hemileia vastatrix, la roya — is a fungus that attacks the leaves, defoliates the plant, and destroys its ability to ripen fruit.
Why it matters so much
Arabica descends from a tiny founding population and is genetically narrow, which makes it broadly susceptible.
Rust destroyed Ceylon’s coffee industry in the 1870s — which is why Sri Lanka grows tea. It reached the Americas in 1970 and caused a regional crisis from 2012, cutting Central American production severely and driving migration.
What it does to the cup, indirectly
Resistance breeding is the main defence, and resistant hybrids — Catimor, Sarchimor, Castillo, Lempira — carry robusta genetics, which generally costs cup quality.
Farmers face a real choice: plant Caturra and risk the crop, or plant Castillo and lose a few points of score.
Newer generations of resistant varieties have closed much of that gap, and Colombia’s Castillo in particular now cups well when grown carefully.
Climate change
Rust thrives in warmth and humidity, and it is now appearing at altitudes that were previously too cool. That is squeezing the high-altitude land arabica depends on.
What it means for a drinker
Prices and availability move with rust outbreaks, and the varietal on your bag is often the result of this pressure rather than a free choice.
Last reviewed 8 August 2026