What is coffee leaf rust?

Coffee leaf rust — 'roya' in Spanish — is a fungal disease caused by Hemileia vastatrix. It produces orange spots on the underside of leaves, triggers defoliation, weakens the plant and can wipe out a harvest. First identified in Sri Lanka in 1869, it remains the single biggest biological threat to Arabica coffee worldwide.

Hemileia vastatrix is an obligate biotroph, meaning it only survives on a living host. Its cycle, described in the nineteenth century after the destruction of Ceylon's coffee industry, starts when a urediniospore lands on a wet leaf; it germinates in 24 to 48 hours and penetrates through stomata. Two to three weeks later, yellow and then orange-rust spots emerge on the underside of the leaf, releasing millions of spores carried by wind and raindrops. Optimal temperatures sit between 21 and 25 °C with high humidity — precisely the conditions that expand as the climate warms and as producers descend to or remain below 1,400 m.

The economic and human toll is heavy. The 2012-2013 Central American crisis (Guatemala, Honduras, Nicaragua, El Salvador, Costa Rica) became known regionally simply as 'la roya': up to 30 % of the harvest lost according to FAO estimates, nearly 400,000 direct jobs affected and many families forced into migration. In Brazil in 2020-2021, rust stacked on top of frost and drought compounded the shock. Historically, it was rust that drove Ceylon to convert its coffee plantations into tea in the late 1800s — one reason Sri Lanka is now a tea country rather than a coffee one.

Responses are multi-layered. Copper- and triazole-based fungicides dominate on conventional farms, though effectiveness is partial and raises health and environmental concerns. Resistant varieties: Catimor (a Caturra × Timor Hybrid cross carrying Coffea canephora genes), Sarchimor, and then the newer F1 hybrids from World Coffee Research such as Centroamericano or Starmaya, alongside Kenya's Ruiru 11, all combining rust tolerance with cup quality well above the early Catimors. Moderate agroforestry: balanced shade can lower disease pressure by regulating leaf humidity. In Belgium, the specialty scene is pulling these resistant lots onto its menus — Centroamericano or Starmaya microlots increasingly feature at Brussels and Ghent roasters, and occasionally surface on the coffee lists of La Hulpe or Genval.

Coffee leaf rust at a glance