At the mention of the fungus with the botanical name Hemileia Vastatrix, shoulders shudder. Roya, coffee rust, coffee leaf rust is one of the worst and most feared fungal diseases on a coffee farm, whose outbreak has devastating consequences. It is responsible for millions of dollars in damage annually, and it can even destroy entire harvests. The fatal part: coffee rust can spread through wind and by humans. But let's take this one step at a time.
What is coffee rust?
Coffee rust, or in Spanish la roya or in English coffee leaf rust, is caused by the fungus Hemileia Vastatrix and is recognizable by orange pustules on the underside of the leaves of a coffee plant. If a leaf has only a few of the round, rust-colored spots, it can continue to function more or less normally. However, if the environment promotes the development of Hemileia Vastatrix, it becomes difficult for the leaves to supply the plant with the nutrients it needs. Heavily infested leaves subsequently die off.
The fungus only attacks the coffee leaves, but it damages entire plants. Due to the missing leaves, the coffee plant has only limited ability to carry out photosynthesis, which means that in the year of infestation, due to a lack of nutrients, it can produce up to 50% fewer flowers and correspondingly fewer coffee cherries.
A distinction is made between primary and secondary loss
Primary loss refers to the crop loss that occurs in the year of initial infestation. The defoliated coffee shrub can no longer supply the plant with sufficient nutrients, the branches and cherries cannot develop properly.
In the following year, one speaks of secondary loss, which can be even more dramatic. After an outbreak in the year of initial infestation, it looks as though the coffee plants might recover—because in the next season it can produce leaves again. But damaged or dried and therefore dead branches can no longer produce cherries. Studies in Central America have shown that primary loss can amount to up to 26%. With secondary loss, crop losses of up to 36% are reported.
Coffee rust thus interrupts the delicate balance of nutrient supply
Hemileia Vastatrix makes entire coffee regions look like rows of skeletons and destroys the livelihoods of millions of coffee workers. As if the tragic scale of a coffee rust outbreak were not enough, the fungus also spreads with ease throughout the world.
In the 2012/13 and 2013/14 harvest seasons, the worst outbreak to date, also known as "The Big Rust," global losses rose to 600 million dollars. Or in other words: over 300,000 people lost their jobs due to insufficient harvests.
How does coffee rust spread?
The basic conditions for roya can be explained using a triangle. To create optimal conditions for the fungus to develop, three elements are needed:
- The right environment. Temperatures of optimal 21-25°C promote the spread of coffee rust, but it also thrives well with temperatures of 15-28°C. When a hot and humid phase follows a rainy period, the conditions are ideal. Coffee rust needs water droplets on the leaves to germinate. So if it is hot and dry, this is not a good environment for the development of Hemileia Vastatrix.
- The host. Coffea Arabica in particular is the sought-after host for the fungus. Coffea Canephora as well as Coffea Liberica and some varieties of Coffea Arabica are currently still resistant to coffee rust.
- The pathogen. If the environment is suitable and the host is present, there still needs to be a pathogen. If coffee rust is present in the region, the triangle is complete.
If coffee rust is present in a region, it happens incredibly quickly. The most common method of spread is wind, which can carry spores many kilometers. But it is also spread by birds and insects as well as by travelers on ships, trains, and even airplanes. At the beginning of the spread of Hemileia Vastatrix, workers carried the spores on their bodies and clothes, spreading it from coffee land to coffee land.
On a single centimeter of an infected leaf, you can find up to 120,000 to 150,000 spores—an almost unimaginable number.
A reinforcing factor in the spread of coffee rust is also the very low genetic diversity in Coffea Arabica. Most Arabica varieties trace their genes back to Typica or Bourbon, which also means that they are all susceptible to the same diseases and fungi.
Hemileia Vastatrix has the ability to constantly adapt to new environments, comparable to flu viruses in humans, and repeatedly mutate. Many of the varieties that were still resistant 10 years ago are now susceptible to this existential threat fungus. Higher temperatures, increased rainfall, extreme winds, and increased human mobility are some of the factors that have contributed to this.
Coffee rust. The history. The world map.
The coffee world watched with panic as every corner of the Indian Ocean basin was affected by coffee rust in the 1950s. Hemileia Vastatrix continued its devastating conquest to West Africa and finally arrived in the 1970s in the vast coffee farms of Latin America. By 1990, it had spread to every major coffee region. However, it seemed as though coffee rust could be kept under control with adequate care and resistant varieties that many farmers began to plant—coffee rust was, so to speak, a controllable nuisance.
Hemileia Vastatrix was already present before 1870 in the rainforests of Ethiopia, which is considered by many as the cradle of the coffee plant. At that time, there were hundreds of Coffea species and varieties, and just as many diseases and fungi. But in harmony with nature and the handling and structure of coffee production at that time, an infestation of a variety by the destructive fungus or another disease had no significant impact on the ecosystem and prevented a potential outbreak.
High biodiversity can stop coffee rust. But in monocultures, it spreads rapidly.
From the tropical hot and humid weather of Ethiopia, coffee was brought by the Ottomans to Yemen and grown there for the first time on a large scale. Whether they brought coffee plants and thus also coffee rust, or whether they only brought seeds, is not entirely clear. It is quite possible that coffee rust never came to Yemen, since Hemileia Vastatrix clings to coffee leaves and is not spread through seeds. In any case, the weather in Yemen was hot and dry, and thus not a good basis for the development of coffee rust and other diseases that cannot survive in this climate. The climate in Yemen was essentially a natural preventative of a coffee rust outbreak, and so the devastating fungus remained undiscovered.
From Yemen, Coffea Arabica was spread throughout the world by the colonial powers France, Great Britain, and the Netherlands. Thus the dormant monster was given new fertile ground through favorable weather conditions. The Dutch brought coffee from Yemen to India and from there around 1800 to Ceylon, today's Sri Lanka. Soon after, the Dutch were driven out by the British, who immediately planted extensive coffee fields to make a lot of money.
Ceylon—a ticking time bomb
Coffee rust was first formally documented in 1861 in Sri Lanka (formerly Ceylon), where it thrived in warm temperatures and extended rainfall and destroyed the entire coffee cultivation—by the end of 1880, most farmers had switched from growing coffee to tea (which also explains why Sri Lanka is such a major tea nation today).
The large-scale coffee farms were all attacked by coffee rust. Billions of fungal spores rose into the air and were distributed through air currents, by humans and through ship transport, by birds and insects, and especially by wind to large parts of the world. By the 1950s, coffee rust had reached the entire Indian Ocean basin—except for Yemen. Coffee rust contributed to the (temporary) decline of coffee production in Asia and the Pacific. While these regions made up ⅓ of total production in the early 19th century, 100 years later it was only 5%.
From the mid-1950s to mid-1980s, the epidemic broke out in West Africa and was first discovered on a farm in Bahia, Brazil in 1970. From there it continued to spread and reached Central America in the 1970s. Discovered in Nicaragua in 1976, Hemileia Vastatrix had arrived in almost every corner of Central America by the 1990s.
The 3 phases of coffee rust outbreak
The history of coffee rust is historically divided into three phases.
The first phase, the colonial phase, lasted from 1869 to approximately 1945 and included the first major coffee rust outbreak in the eastern hemisphere. In this phase, the spread of the fungus Hemileia Vastatrix was driven by the mobility of colonial powers and their exchange of enslaved people for harvest work.
The second phase, the developmentalist phase, describes the period from approximately 1950-1990, characterized by World War II and the Cold War. Global coffee trade was heavily regulated by the International Coffee Agreement (ICA) during this time. In order to keep prices relatively high and stable, the ICA set export regulations for each country. States took on a larger role in marketing their national coffee than they had in the colonial phase. For example, they supported farmers with technical and financial means and pursued various development projects for social and political stability.
Global distribution of the coffee rust, 1952. This map also reflects the global distribution of Arabica and Robusta coffee at the time. Most countries east of the line produced Robusta, while those west of the line produced Arabica. Coffee Areas of the World in Relation to Rust Disease. 1952. Foreign Agriculture 16:160.
Published in: Stuart McCook; John Vandermeer; Phytopathology® 2015, 105, 1164-1173.
Copyright © 2015 The American Phytopathological Society • DOI: 10.1094/PHYTO-04-15-0085-RVW
The third phase, also the neoliberal phase, designates the period from the late 1980s to today. An incredibly destructive series beginning in Colombia is known under the name The Big Rust, which reached its negative peak in the 2012/13 and 2013/14 harvest seasons in Central America.
In 2008, Colombia produced 31% less coffee than the previous year. The epidemic spread further northward through Central America to Mexico, then back southward, finally reaching Peru and Ecuador in 2013/2014. The International Coffee Organization estimates that coffee production in Central America in the 2012/13 and 2013/14 harvest years cost more than 616 million dollars.
In contrast to previous outbreaks in recent decades, the Big Rust was not triggered by a carrier brought into an area where coffee rust did not previously exist. It was rather driven by extreme weather conditions that favored the development of the fungus.
The "Big Rust" in Latin America since 2008.
Published in: Stuart McCook; John Vandermeer; Phytopathology® 2015, 105, 1164-1173.
Copyright © 2015 The American Phytopathological Society • DOI: 10.1094/PHYTO-04-15-0085-RVW
Conclusion on coffee rust
Hemileia Vastatrix constantly adapts to new conditions
The ecosystem as well as the economy are in constant change, and of course so is coffee rust, which, like flu viruses, continuously mutates. This means that coexistence with Hemileia Vastatrix is always a snapshot and can change at any time. For example, it is now much hotter in the upper regions than it was just a few years ago. While our partners at Finca El Arbol once had a daily maximum of around 25°C at Easter, the hottest time of the year in Nicaragua, temperatures today rise to 35°C or higher.
Unstable market—catalyst for roya
There are also the challenges of the stock exchange, which keeps prices unstable and makes long-term planning impossible. When prices are too low and the coffee farmer cannot work at cost-covering rates, let alone invest money in the renewal of coffee plants, care of the coffee farm, or in combating Hemileia Vastatrix or diseases, he must abandon his farm. The land becomes overgrown, and coffee rust spreads unchecked.
Roya increases the cost of coffee production
The control of Hemileia Vastatrix has greatly increased the cost of coffee production. At low prices, farmers cannot afford control and must abandon their farm, leave rural life, and build a new life elsewhere.
Roya shaped the coffee world as it is today
Coffee rust has only marginally reduced the global coffee supply, but it has shaped global trade in other ways. After 1900, the Dutch invested in the development of the resistant species Coffea Canephora, which soon stirred up global coffee affairs and today makes up about 40% of coffee production. The plant, which was originally developed as a response to coffee rust, transformed and shaped the structure of global coffee production and consumption in the 20th century. But more on that another time.
Further reading
https://www.youtube.com/watch?v=gnPChFLHWA4
https://perfectdailygrind.com/es/2021/01/13/roya-del-cafe-por-que-es-nociva-y-como-controlar-su-propagacion/
https://apsjournals.apsnet.org/doi/10.1094/PHYTO-04-15-0085-RVW#fig1
Stuart McCook, 2019, Coffee is not forever
