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

How a fungal disease reshaped specialty coffee supply

Coffee leaf rust's emergence as a serious threat to specialty Arabica production in Central America traces a specific historical trajectory. Hemileia vastatrix — the fungal pathogen responsible — had been present in Latin America since its inadvertent introduction from Africa in the 1970s, causing occasional outbreaks but remaining manageable through fungicide application and the resistance of certain commercial varieties. The 2012–2013 epidemic that devastated production across Guatemala, Honduras, El Salvador, Costa Rica and Mexico was different in scale: unusually warm and wet conditions that year created a perfect fungal growth environment, and the epidemic spread across all altitude bands simultaneously rather than being contained to vulnerable lowlands. Some Central American specialty coffee farms lost 50–70% of their harvest in a single season.

The specialty coffee quality impact of the leaf rust epidemic was immediate and substantial. Reduced harvests from high-altitude specialty farms meant less supply of quality lots available for premium specialty markets — prices rose as supply contracted, and some roasters found their established sourcing relationships temporarily unable to deliver committed volumes. The epidemic also accelerated the already-underway research into resistant varieties: World Coffee Research's investment in F1 hybrid development increased significantly in the epidemic's aftermath, driven by the recognition that commercial varieties' susceptibility to rust was a systemic supply chain vulnerability that quality premiums alone couldn't resolve.

Going deeper

The 2026 situation with coffee leaf rust has improved in some regions and deteriorated in others. The widespread deployment of resistant varieties — Marsellesa, Centroamericano and various H1 hybrids — in Honduras and Guatemala has reduced epidemic vulnerability in farms that have transitioned. But climate change's disruption of temperature and rainfall patterns continues to create new rust pressure conditions, and resistant varieties' practical performance varies by specific rust strain, altitude and farm management practices. The specialty coffee industry's response — investing in variety research, supporting farm transition to resistant varieties, and building climate adaptation capacity — represents the most significant agricultural development investment the specialty sector has ever undertaken, motivated by the existential supply risk that 2012–2013 made undeniable.